Type species.—Pentagnostus anabarensis Lermontova, 1940, from the Anabar region (exact location or formation not listed on specimen labels or in text; E.L. Naimark, personal communication, 2017), Siberia, by original designation.

Diagnosis.—See Laurie (2004).

1938a Agnostus bonnerensis Resser, p. 6, pl. 1, figs. 16, 17.

1939a Agnostus bonnerensis; Resser, p. 8, pl. 2, figs. 24–26.

1939a Vistoia? minuta Resser, p. 21, pl. 2, fig. 1 only.

1979 Peronopsis bonnerensis; Palmer and Halley, p. 76, pl. 12, figs. 11, 15.

2012 Pentagnostus (Meragnostus) bonnerensis; Naimark, figs. 16a, b.

2018 Pentagnostus brighamensis; Sundberg, p. 6, fig. 6.1–6.16.

Holotype.—Pygidium USNM 156547 from USNM loc. 37n.

Paratypes.—USNM 156548, 156548a, 95025–95025c from USNM loc. 37n.

Diagnosis.—Cephalon with low inflation; preglabellar median furrow absent, glabella well defined and gently sloping downward from weakly developed median node to frontal lobe; anterior lobe subrectangular, well defined with moderately deep and straight F3 furrow. Pygidium with low inflation; axial lobe well defined with deep axial furrows, moderately long; well-developed F1 furrow, directed anterolaterally, shallower medially; F2 furrow shallow to nearly effaced, straight to bending slightly posteriorly; moderate size median tubercle, with highest portion at posterior margin of M2; M3 with low convexity; terminus bluntly rounded, reaching the posterior border furrow in smaller specimens, nearly reaching the furrow in larger specimens; shallow to moderate postaxial median furrow in smaller specimens; border relatively wide (trans, sag.), with small marginal spines.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Spence Shale (Glossopleura walcotti Zone), Two Mile Canyon, Malad Range and Wasatch Mountains, Utah (Resser, 1939a; Campbell, 1974). Red Pass Limestone member, Carrara Formation (Mexicella mexicana Zone), Belted Range, Nevada (Palmer and Halley, 1979). Emigrant Formation (Glossopleura walcotti/Ptychagnostus praecurrens Zone), Split Mountain, Nevada (Sundberg, 2018).

Description.—Cephalon (N = 11) and pygidium (N = 20) 3.5 to 4.4 mm long; nonscrobiculate; surface smooth. Cephalon rounded to weakly subquadrate, 91 ± 4% as long as wide, nonspinose, low inflation; border narrow, slightly convex; border furrow well developed, very narrow; preglabellar median furrow absent. Glabella well defined by moderately deep axial furrow, gently down sloping from weakly developed median node to frontal lobe, length 67 ± 3% as long as cephalon; anterior lobe well defined, subrectangular, rounded anteriorly, occupying 33 ± 3% of glabellar length. F3 furrow well defined, straight or bowed slightly anteriorly; posterior glabellar lobe subrectangular with very weak taper, moderately inflated in its posterior half, F2 furrows very weakly developed as faint notches indenting lobe margin. F1 furrows very weakly developed as slight indentations about level with anterior extremities of basal lobes; glabellar node located about midway between F1 and F2 furrows; basal lobes small, with a broad (tr.) bulbous posterior portion and a narrow (tr.), depressed anterior portion.

Hypostome unknown.

Pygidium rounded to weakly quadrate, 90 ± 3% as long as wide, low inflation, with small posterolateral spines; border of moderate width, wider posteriorly, flattened; border furrow distinct, narrow; postaxial median furrow variably developed, ranging from broad and clearly defined in smaller specimens to only being evident anteriorly to absent in larger specimens. Axis well defined with deep axial furrows, 68 ± 4% as wide as long and 74 ± 4% of pygidial length, constricted across F2, posteriorly angular to slightly rounded, moderately low convexity. F1 furrow strong laterally and shallower medially; bent anteriorly. M1 lobe width 45 ± 3% pygidial width, lateral margins convex, converging posteriorly. F2 furrow shallow to nearly effaced; straight or bending slightly posteriorly; M2 lobe constricted with margins slightly convex and converging slightly anteriorly. Axial node of moderate size, slightly elongate, highest at posterior margin of M2. Posteroaxis (M3) with low convexity, occupying 50 ± 4% of axial length, with maximum width 41 ± 3% pygidial width near anterior extremity of lobe; terminus angular to slightly rounded, reaching the posterior border furrow in smaller specimens, nearly reaching the furrow in larger specimens.

Remarks.—Resser (1938a) provided no differential diagnosis, only a comment that its characteristics “place it between A. montis Matthew [1899]…and A. interstrictus White [1874]…” (Resser, 1938a, p. 6) and that it was similar to an undescribed species from the Spence Shale, but differed in having an axial furrow on the pygidium.

Pentagnostus bonnerensis is similar to P. brighamensis from the Spence Shale, but differs in the pygidium having a higher convexity, longer axis that nearly reaches the border furrow, with the posterior lobe as wide as the M1, F1 nearly effaced, and F2 nearly effaced and curved posteriorly. Both species have poorly developed posterolateral nodes (Robison, 1978, pl. 1, figs 7, 11, 14), with P. bonnerensis having slightly weaker nodes (Figs. 6, 7; arrows). Sundberg (2018) also stated that the two species differed in that P. bonnerensis lacked a postaxial median furrow. However, topotypes of P. bonnerensis show a strongly to weakly developed postaxial median furrow in smaller specimens (Fig. 7.22, 7.23). Resser (1939b, p. 8) mentioned the “more circular outline for both shields” in the latter species, but this could be the result of compression in shale. However, limestone/silicified specimens (Robison, 1978) have a more elongate cephalon and pygidium when compared to P. bonnerensis.

Pentagnostus bonnerensis is similar to P. lautus (Resser, 1939b) from the Spence Shale, but differs in the pygidium having a shallower F1 and nearly effaced F2, blunter end to the axis, and lacking a post axial furrow. The cropped pictures of Resser (1939b, pl. 2, figs 17, 18) do not show the small marginal spine, but the specimen in the bottom right of Resser (1939b, pl. 2, fig. 16) does illustrate these small spines.

Pentagnostus bonnerensis is similar to ?Euagnostus aff. E. taijiangensis (Huang and Yuan, 1994) of Laurie (2006, p. 148, fig. 20), but differs in the pygidium having a slightly shorter axis that does not reach the border furrow, a slight constriction of the axis at the M2 position, absence of a postaxial median furrow in larger specimens, and a weaker development of the posterolateral spines. Laurie (2006, p. 150) was uncertain about the assignment of his Australian material to ?E. taijiangensis due to the poor preservation of the type material.

Type species.—Agnostus elkedraensis Etheridge, 1902, from the Northern Territory, Australia.

Diagnosis.—See Laurie (2004).

2018 Pentagnostus bonnerensis (Resser, 1938a); Sundberg, p. 9, fig. 7.1–7.3.

Holotype.—Pygidium USNM 724035 from USNM loc. 44283.

Paratypes.—USNM 724025–724034, 724036–724049 from USNM loc. 44283.

Diagnosis.—Cephalon rounded with lateral margins convex; minute, advanced posterolateral spines; a relatively narrow border with narrow, well-defined border furrows. A well-rounded, inflated pygidium with a long axis not reaching border furrow, without secondary pygidial axial node; M3 with expanded, approximately equal to or greater than axial width in larger specimens, moderately rounded termination; minute marginal spines.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Emigrant Formation (Glossopleura walcotti/Ptychagnostus praecurrens Zone), Split Mountain, Nevada (Sundberg, 2018).

Description.—Cephalon (N = 11) and pygidium (N = 12) up to 3.5 mm long, nonscrobiculate, smooth. Cephalon moderately inflated, rounded to weakly subquadrate, 87 ± 4% as long as wide, short posterolateral spines; border narrow, slightly convex; border furrow well developed, very narrow; preglabellar median furrow absent. Glabella well defined by moderately deep axial furrows, 73 ± 2% as long as cephalon, down sloping from top of median node to anterior lobe; anterior lobe well defined, subrectangular, rounded anteriorly, occupying 34 ± 1% of glabellar length; F3 furrow well defined, straight; posterior glabellar lobe subrectangular with very weak forward taper, strongly inflated in its posterior half, F2 furrows very weakly developed as very faint notches indenting lobe margin. F1 furrows very weakly developed as very slight indentations slightly anterior of the basal lobes; glabellar node located about midway between the F1 and F2 furrows; basal lobes small, broad (tr.), bulbous, nearly triangular.

Hypostome and thorax unknown.

Pygidium rounded to weakly quadrate, 90 ± 4% as long as wide, moderately inflated, with minute spines; border of moderate width, narrowing anteriolaterally, slightly convex; border furrow distinct, narrow; postaxial median furrow faint in smaller specimens, absent in medium to larger specimens. Axis well defined by moderately deep furrow, 65 ± 4% as wide as long and 77 ± 6% of pygidial length, constricted across F1, posteriorly variably rounded, moderately convex. F1 furrow very weak laterally and effaced medially; bent anteriorly. M1 lobe width 45 ± 3% pygidial width, lateral margins convex, converging posteriorly. F2 furrow very shallow laterally, effaced medially; bending slightly posteriorly; M2 lobe constricted with margins slightly convex and weakly converging anteriorly. Axial node of moderate size, slightly elongate, highest portion at near midlength of M2. Posteroaxis (M3) with moderate convexity, occupying 51 ± 4% of axial length, with maximum width 44 ± 7% pygidial width near middle of lobe, width 97 ± 11% axial width, with lower proportion (∼80%) in smaller specimens and higher proportion (∼100%) in larger specimens (R² = 0.887; Fig. 9); terminus variably rounded, nearly reaching the border furrow.

Etymology.—Named for the State of Idaho.

Remarks.—Laurie (2004) provided a revised diagnosis of the genus. Some of the key cephalic features in Itagnostus idahoensis n. sp. are the absence of the preglabellar median furrow, semiovate anterior lobe, straight F3, weak to absent F2, and location of the glabellar node. Similar pygidial features include the long axis, broad with semiovate posterior lobe, and nearly effaced axial furrows. Itagnostus idahoensis n. sp. has a cephalon with small posterolateral spines, and pygidia with very small marginal spines, and lacking a postaxial furrow. The list of species assigned to the genus varies among authors (e.g., Laurie, 2004; Naimark, 2012; Naimark and Pegel, 2017), so comparison of I. idahoensis n. sp. is limited to the most similar species.

Itagnostus idahoensis n. sp. is similar to I. montis (Matthew, 1899) from the Stephen Formation (Ehmaniella Zone, Rasetti, 1951). Unfortunately, all specimens of I. montis are flattened in shale (Rasetti, 1951, pl. 25, figs. 11–14), which makes comparison of the two species difficult. Some apparent differences are I. idahoensis n. sp. has a cephalon with a more anteriorly located axial node and posterolateral spines not being advanced, and the pygidium having straighter lateral sides.

Itagnostus idahoensis n. sp. differs from I. elkedraensis (Laurie, 2004, fig. 12) in the cephalon having a broader axis and pygidium with smaller marginal spines and more expanded (trans.) M3. Itagnostus idahoensis n. sp. is very similar to I. walleyae Laurie, 2004, but differs in the cephala having continuous F3 of nearly uniform depth, more advanced, smaller posterolateral spines, and the pygidium having a more inflated lateral profile and lacking a secondary axial node. Itagnostus idahoensis n. sp. differs from I. oepiki Laurie, 2004, in having a more rounded cephalon and pygidium and in lacking a secondary pygidial node.

Type species.—Pagetia bootes Walcott, 1916b, from the Stephen Formation, Mount Field, British Columbia, by original designation.

Diagnosis.—See Jell (1975).

1938a Pagetia fossula Resser, p. 6, pl. 1, figs. 8–11.

1939b Pagetia maladensis Resser (part), p. 25, pl. 2, fig. 4 (part, pygidium in upper right corner), 5 (part, cranidia in upper left and upper center and pygidium at lower right).

1966 Pagetia fossula; Rasetti, p. 507, pl. 59, figs. 22–28.

1966 Pagetia rugosa Rasetti, p. 509, pl. 60, figs. 1–7.

1968 Pagetia arenosa Fritz, p. 189, pl. 43, figs. 10, 11.

1979 Pagetia rugosa; Palmer and Halley, p. 77, pl. 12, figs. 9, 13.

1979 Pagetia sp., Palmer and Halley, p. 77, pl. 12, figs. 10, 14.

2018 Pagetia fossula; Sundberg, p. 16, fig. 10.1–10.12.

2018 Pagetia rugosa; Sundberg, p. 16, fig. 10.13–10.19.

Lectotype.—Here designated, pygidium USNM 95026 from USNM loc. 37n.

Paralectotypes.—Here designated, USNM 95026a–e from USNM loc. 37n.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Upper Langston Formation at Two Mile Canyon, Idaho (Rasetti, 1966; Campbell, 1974). Pyramid Shale member (Mexicella mexicana Zone), Carrara Formation, Belted Range, Nevada (Palmer and Halley, 1979). Pioche Shale (Glossopleura walcotti Zone?), northern Egan Range, Nevada (Fritz, 1968). Emigrant Formation (Glossopleura walcotti/Ptychagnostus praecurrens Zone), Split Mountain, Nevada (Sundberg, 2018).

Remarks.—Sundberg (2018) discussed the co-occurrence of Pagetia fossula Resser, 1938a and P. rugosa Rasetti, 1966 from the Emigrant Formation and the difficulty of separating the cranidia of the two species based on the convexity of the fixigena. The cranidia from the Lakeview Limestone also show a gradation in the convexity of the fixigena; but in addition, the pygidial convexity and development of the pleural furrows used to separate the two species also show a gradational change. As a result, the two species are synonymized here. An interesting difference between the material reported here and Resser's type specimens from the Lakeview Limestone (Rasetti, 1966, pl. 59, figs. 22–28) is the absence of the larger granules on the pleural bands of the pygidium, although one specimen (Rasetti, 1966, pl. 59, fig. 28) appears to also lack these granules.

Remarks.—Considering Corynexochida as a monophyletic group may be in error, and this taxon is probably polyphyletic, as suggested by Robison and Babcock (2011) and Sundberg (2014).

Type species.—Athabaskia ostheimeri Raymond, 1928, from “Middle Cambrian strata at the Columbia Glacier at the head of the Athabaska River, in Alberta…” (Raymond, 1928, p. 312), by original designation.

Diagnosis.—See Lochman (1952).

1938a Clavaspidella minor Resser, 1938a, p. 9, pl. 1, figs. 45, 46, 48, 49; non fig. 47 (= Elrathina idahoensis [Resser, 1938a]).

1952 Athabaskia minor; Lochman, p. 130, pl. 31, figs. 1–3.

Holotype.—Cranidium USNM 95039 from USNM loc. 37n.

Paratypes.—Specimens USNM 95039a–c from USNM loc. 37n. Also included by Resser (1938a, pl. 1, fig. 47) is a librigena USNM 95039d, which belongs to Elrathina idahoensis.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho (Resser, 1938a, 1939a). Arrojos Formation (Lochman, 1952, p. 131; Glossopleura walcotti Zone) or basal Tren Formation (Cooper and Arellano, 1952, p. 19), Arrojos Hills, Sonora, Mexico.

Remarks.—Resser (1938a) assigned a single external mold to the species, which clearly belongs to Elrathina idahoensis based on its small palpebral lobe suture, overall suture outline and short genal spine (Fig. 11.5). Lochman (1952, p. 130–131) reassigned the species to Athabaskia and adequately redescribed the species based on the type specimens. She also reported the species from Sonora, Mexico, locality 800g, which she placed in the Arrojos Formation, but which Cooper and Arellano (1952, p. 19) placed in the Tren Formation. Figured herein are additional specimens, including larger cranidia and pygidia.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho.

Remarks.—Two cranidia occur stratigraphically above A. minor that are very similar except that they have occipital spines. No pygidia belonging to the genus were found, thus the taxonomic placement of the taxon is left open.

Remarks.—Several rostral plates/hypostomes were found in almost all horizons. Given that none of the specimens is directly associated (articulated) with cranidia, their specific affiliation cannot be assessed and they are left in open nomenclature. The characteristics of these specimens suggest that they belong to Dolichometopidae, being similar to hypostomes of Wenchemnia Resser, 1951 (see Sundberg, 1994). Athabaskia minor is the only species of this family found in the area studied. Whereas the cranidia of this species do attain the size to accommodate the hypostome, this species is relatively rare in the samples and cannot be definitely assigned to the hypostome. In addition, the hypostomes are also similar to Parkaspis Rasetti, 1951 (see Sundberg, 1994), which is assigned to Zacanthoididae (Sundberg, 1994). This family is only represented by Zacanthoides sampsoni Resser, 1938a in the Lakeview Limestone, a species that does not attain the cranidial size to accommodate the largest hypostome found.

Type species.—Bathyuriscus (Kootenia) dawsoni Walcott, 1889, from the Stephen Formation, Mount Stephen, British Columbia, by original designation.

Diagnosis.—See Sundberg (1994).

Remarks.—Over 100 species of Kootenia are named (see Palmer and Halley, 1979; Sundberg, 1994) and the group is in need of revision. One of the key characteristics is the features of the pygidia, especially the number of pygidial spine pairs. Resser (1939b) named 12 species of Kootenia from the age-equivalent Ptarmigania strata (= Spence Shale, Langston Formation) of northern Utah. These species have a range in pygidial spines from five to seven pairs. The pygidia from the Lakeview Limestone have five pairs of spines that curve upward. A single specimen (Fig. 14.9) has only four pairs of spines, lacking the terminal two smaller spines. Of Resser's (1939b) 12 species, five have five pairs of spines, K. convoluta, K. maladensis, K. granulosa, K. bearensis, and K. pectenoides. Of these, the most similar to the Lakeview Limestone specimens is K. bearensis, which is only known from pygidia. All of the species named by Resser (1939b) that are known from cranidia as well have strongly inflated glabella and, in larger specimens, suboval shapes. This is in sharp contrast to the specimens from the Lakeview Limestone, which have lower inflation of the glabella (Fig. 14.2) and a more expanding glabella (Fig. 14.1, 14.4, 14.6). A single large cranidium (Fig. 14.10) has a more oval glabella. As a result of the differences in pygidia spine pairs (four versus five) and glabella shape (suboval versus expanding), it is possible that two species are represented in the Lakeview Limestone. Given the potential mixture of two species and the specimens being generally incompletely preserved and very rare, the specimens from the Lakeview Limestone are left in open nomenclature.

Type species.—Oryctocara geikiei Walcott, 1908, from the Spence Shale, Danish Flat, Idaho, by original designation.

Diagnosis.—See Whittington (1995).

1908 Oryctocara geikiei Walcott, p. 23, pl. 1, figs. 9, 10.

1938a Oryctocephalus walcotti Resser, p. 9, pl. 1, fig. 22 (only).

1938a Utia curio Walcott; Resser, p. 9, pl. 1, fig. 21 (only).

1939a Oryctocara geikiei; Resser, p. 21, pl. 1, pl. 2, figs. 22, 23.

1995 Oryctocara geikiei; Whittington, p. 556, pl. 4, figs. 2–9.

2015 Oryctocara geikiei; Robison et al., fig. 122.

Lectotype.—Shield USNM 53426, 53428 (part, counterpart), Spence Shale, Spence Gulch, Idaho.

Paralectotype.—Pygidium USNM 53427, Spence Shale, Spence Gulch, Idaho.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho (Resser, 1938a, 1939a). Spence Shale (Glossopleura walcotti Zone), Liberty Canyon and Two Mile Canyon, Idaho (Walcott, 1908; Campbell, 1974; Whittington, 1995) and Wellsville Mountains, Utah (Campbell, 1974; Robison et al., 2015). Stephen Formation (Glossopleura walcotti Zone), Mt. Stephen, Canada (Whittington, 1995).

Remarks.—Whittington (1995) provided an extensive description of Oryctocara geikiei as well as assigning a lectotype specimen. Resser (1938a, pl. 1, fig. 22) misidentified the cranidium of O. geikiei as that of Oryctocephalites walcotti (Resser, 1938a; paratype USNM 95038a) and the pygidium (p. 1, fig. 21, USNM 95041b) as that of Utia curio Walcott, 1924. Whittington (1995, pl. 4, figs. 2, 4) reassigned and re-illustrated the cranidium USNM 95041a and questionably the pygidium to O. geikiei (Fig. 15.28); however, additional pygidia from this study show that the pygidium belongs to O. geikiei.

Whittington (1995) reported 11–12 thoracic segments and six (?) pygidial axial rings and a terminal piece. None of the specimens from the Lakeview Limestone is known from completely articulated shields. The single specimen of articulated thorax and pygidium has 10 thoracic segments. Isolated pygidia have potentially a fused thoracic segment based on fragmentation (Fig. 15.26, 15.29) and exposure of the articulating ring(s) (Fig. 15.20–15.23, 15.26). Complicating this situation is that the pygidial axial rings commonly have a shallow furrow separating the anterior and posterior portion of each ring. These features are also seen in species of Arthricocephalus Bergeron, 1899, Oryctocarella Tomashpolskaya and Karpinski, 1961, and Ovatoryctocara Chernysheva, 1962 (see Geyer and Peel, 2011; Peng et al., 2017, which is referred to as a partially released segment of the transitory pygidium). As a result, pygidia range from three to seven (Fig. 16) axial rings plus a terminal piece, unless the “thoracic segment” is fused to the pygidium, then the range would be four to eight axial rings plus a terminal piece. The broad distribution of the number of axial rings across a range of sizes suggests that axial ring count is not fixed in meraspids or holaspids and cannot be used as a specific or generic diagnosis.

The ontogeny of O. geikiei from the Lakeview Limestone is represented by disarticulated material, thus meraspid degrees cannot be assigned, nor can the transition between meraspids and holaspids. In general, the smallest meraspid cranidium questionably assigned to this species (Fig. 15.1) has a narrow, parallel-sided glabella with a triangular expanding frontal lobe, faint transglabellar furrows, and a proparian suture similar to Ovatoryctocara granulata Chernysheva, 1962 and O. yaxiensis Yuan et al., 2009 (Geyer and Peel, 2011, figs.16G, 16U, 17H). Slightly larger meraspids (Fig. 15.2–15.6) have granules, expanding medial portion of the glabella, more parallel-sided frontal lobe, well-developed transglabellar furrows, some development of the longitudinal furrows and moderately to strongly developed glabellar pits, and palpebral lobes angled adaxially from the glabella forming a wider, posterior portion of the palpebral area of the fixigena. Larger cranidia (Fig. 15.7–15.17) have well-developed anterior and posterior borders, more parallel-sided glabella with well-developed S1 and S2 transglabellar furrows, weak S3 transglabellar furrow, well-developed glabellar pits, S3 pit slit-shaped, lateral glabellar furrows connecting to glabellar furrows at the S1 and S3 positions, palpebral lobes nearly parallel to glabella forming a narrow palpebral area of the fixigena, and a gonatoparian facial suture.

Smallest pygidia have a medial inbend on the posterior margin, pygidial axis that reaches the posterior margin, well-developed plural furrows, weakly developed interpleural furrows (Fig. 15.18). A slightly larger specimen (Fig. 15.19) has scattered granules on the pleural field, slight medial indentation of the posterior margin, pygidial axis that does not reach the posterior margin, and well-developed plural and inter pleural furrows. Larger specimens (Fig. 15.20–15.29) have relatively shorter axes, and a smoothly rounded posterior margin.

Type species.—Vistoia? minuta Resser, 1939a, from the Spence Shale, Bear River Range, Idaho.

Diagnosis.—See Robison and Campbell (1974).

Remarks.—Robison and Campbell (1974) tentatively assigned Thoracocare to Oryctocephalidae based on features of the meraspides of Oryctocara. Sundberg (2018) supported this assignment.

1939a Vistoia? minuta Resser, p. 21, pl. 2, fig. 2; non pl. 2, fig. 1 (= Pentagnostus bonnerensis).

1974 Thoracocare minuta; Robison and Campbell, p. 274, figs. 1, 2B, 2C.

2015 Thoracocare minuta; Robison et al., fig. 139.

Holotype.—Pygidium USNM 188551 from USNM loc. 55c. Robison and Campbell (1974) list this locality as 96511, which is the original lot number for the type specimens.

Paratypes.—Two pygidia under USNM 96511 (original type lot) and pygidium USNM 188194 (originally part of type lot, figured by Robison and Campbell, 1974, fig 2.C) from USNM loc. 55c.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Spence Shale (Glossopleura walcotti Zone), Bear River Range, Malad Range, and Oneida Narrows, Idaho, Wasatch Mountains, Utah (Campbell, 1974; Robison and Campbell, 1974).

Remarks.—The few cranidia and pygidia of Thoracocare minuta from the Lakeview Limestone are similar in size and morphology to the age-equivalent specimens from the Mexicella mexicana and Glossopleura walcotti zones, Spence Shale, Utah (Robison and Campbell, 1974). Sundberg (2018) discussed the differences between Robison and Campbell's (1974) specimens and T. cf. T. minuta from the Emigrant Formation, Nevada, which are larger and the differences may be the result ontogenetic changes.

Thoracocare idahoensis (Resser, 1939b) (see Robison and Campbell, 1974, for additional information), also from the Glossopleura walcotti Zone, Spence Shale, Utah, differs from the Lakeview Limestone specimens in having cranidium with effaced cranidial furrows and wider fixigenae and pygidia that have better defined pleural and interpleural furrows. Robison and Campbell (1974) distinguished the two species also by the length-to-width ratio of the pygidia; measurements from their illustrated specimens, however, do not support this distinction (see Sundberg, 2018).

Type species.—Oryctocephalites typicalis Resser, 1939b, from the Spence Shale, Wasatch Mountains, Idaho, by original designation.

Diagnosis.—See Sundberg (2014).

1899 Oryctocephalus reynoldsi Reed, p. 359, text fig. (line drawing).

1908 Oryctocephalus reynoldsi; Walcott, pl. 3, fig. 1.

1938a Oryctocephalus walcotti Resser, p. 6, pl. 1, fig. 23; non pl. 1, fig. 22 (= Oryctocara geikiei).

1939a Oryctocephalus walcotti; Resser, p. 13, pl. 2, figs. 15–18.

1951 Oryctocephalus reynoldsi; Rasetti, p. 193, pl. 29, figs. 4, 5.

non Oryctocephalus reynoldsi; Shergold, p. 18, pl. 3, figs.

1969 1–6.

1995 Oryctocephalus reynoldsi; Whittington, p. 548, pl. 1, figs. 1, 3–6.

2000 Oryctocephalites walcotti; Sundberg, figs. 4a, 6.

2015 Oryctocephalus walcotti; Robison et al., fig. 123.

Holotype.—Shield A1425 (Sedgwick Museum), Stephen Formation, Mt. Stephen, Canada.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Spence Shale, southern Idaho (Resser, 1939a) and Wellsville Mountains, Utah (Campbell, 1974; Robison et al., 2015). Stephen Formation (Glossopleura walcotti and Ehmaniella zones), Mt. Stephen, Canada (Whittington, 1995).

Remarks.—Oryctocephalus walcotti Resser, 1938a, O. reynoldsiformis (Lermontova, 1940), O. reynoldsi (Reed, 1899), and O. burgessensis (Resser, 1938b) form the crown group of the Oryctocephalites subclade (Sundberg, 2014, fig. 3). However, based on the new material from the Lakeview Limestone, Oryctocephalus walcotti is here reassigned to Oryctocephalites reynoldsi. This reassignment is based on: (1) cranidial features, including an expanding glabella, bluntly rounded frontal lobe, nearly straight and relatively flat anterior border, and relatively weak ocular ridges; (2) librigenal features, including flat lateral border, slightly advanced genal spine, long and relatively narrow genal spine; and (3) pygidial features, including five axial rings, six pygidial spines that are broad based but rapidly narrow to points, three uniform pairs of anterior spines, macrospine that are relatively long, and two pairs of posterior spines that are shorter than the other pygidial spines, poorly developed interplural furrows in anterior segments, then well-defined furrows in posterior segment. These similarities are outlined here due to the Lakeview Limestone specimens, being preserved in limestone, providing less-compressed samples and the type and other specimens are from the Stephen Formation, which are very compressed.

Whittington (1995) redescribed the species based on the flattened specimens from the Burgess Shale. Slight modifications to the description include: the glabella expands from the occipital ring to the L3 position and then slightly narrows, faint S4 furrows are present in all size specimens, the anterior three pairs of pygidial spines and the macropleural spines dorsally flexed.

Sundberg (2000) discussed Oryctocephalites walcotti from the Spence Shale. These specimens are here assigned to O. reynoldsi.

Shergold (1969) reported O. reynoldsi from the Sandover Beds, Arthur Creek Beds, and Beetle Creek Formation, Australia, but these shale specimens differ in having cranidia with slightly narrower (tr.) fixigena (Fig. 20) and pygidia with well-developed interpleural furrows between the three anterior segments and broader pygidial spines in larger specimens. These features are similar to O. reynoldsiformis, particularly the higher stratigraphic position of the Siberian species (see below).

Lermontova (1940, p. 138) described Oryctocephalites reynoldsiformis from the Kuonamka Formation, Kounamkites Zone, as “resembles Oryctocephalus reynoldsi Reed but its glabella has only posterior pair of furrows connected by transversal furrow. There are longitudinal furrows between pits. Palpebral lobes longer, begin almost from occipital furrow” [translation provided by T. Pegel']. These differences between the two species are incorrect, both have only an S1 transglabellar furrow, the smaller specimens have longitudinal furrows between the pits, and the palpebral lobes are of equal length (exsag.) (Lermontova, 1940, pl. 42, figs. 2, 2a, 2b; Fig. 18.4, 18.10, 18.14). However, differences between O. reynoldsi and O. reynoldsiformis occur in the pygidium, which the latter has only two segments anterior of the macropleural spine that have well-defined interpleural furrows (Lermontova, 1940, pl. 42, figs. 2c–e). These differences are not the result of ontogeny; small pygidia of O. reynoldsi (Fig. 18.17–18.21) have three anterior pygidial segments with poorly defined interpleural furrows. Korovnikov and Shabanov (2008, pl. 3, figs. 5, 6) and Shabanov et al. (2008; same specimens) illustrated a well-preserved cranidium and pygidium of O. reynoldsiformis from stratigraphically lower Ovatoryctocara Zone of the Kuonomka Formation. In comparison to O. reynoldsi, the cranidium (pl. 3, fig. 5) has a more pronounced S1 transglabellar furrow and a more convex anterior border and the pygidium (pl. 3, fig. 6) has better defined interpleural furrows and only five pairs of marginal spines. Egorova et al. (1976) illustrated several specimens of O. reynoldsiformis from the Kounamkites Zone of the Kuonomka Formation. Several pygidia appear to be the same as the type specimens (Egorova et al., 1976, pl. 48, figs. 19, 21–23, pl. 49, figs. 17, 18; most photographs are too small to see the necessary details). However, the specimen illustrated by Egorova et al. (1976, pl. 51, fig. 7, and possibly pl. 52, fig. 1) from an interval slightly higher in the section (∼1 m), clearly has three anterior segments similar to O. reynoldsi, but still has well-defined interpleural lobes.

Remarks.—A partly articulated rostral plate and hypostome was found occurring with O. reynoldsi at USNM loc. 44283. It is similar to the rostral plate and hypostome assigned to the species (Fig. 18.12), but differs in having a longer rostral plate, more oval median body, shallower macula, and possibly a weaker suture between the two sclerites. There are no other oryctocephalids know from this locality, so the nomenclature is left open.

Type species.—Embolimus spinosus Rominger, 1887, from the Stephen Formation, Mount Stephen, British Columbia.

Diagnosis.—See Sundberg (1994).

1938a Zacanthoides sampsoni Resser, p. 6, pl. 1, figs. 16, 17.

Holotype.—Shield USNM 95042 from USNM loc. 37n.

Paratypes.—Specimens USNM 95042a–c from USNM loc. 37n.

Diagnosis.—Cranidium having strongly divergent anterior facial sutures ranging ∼70° to an exsagittal line, frontal area lacking plectrum, fine granular ornamentation, glabellar expansion of ∼125% of glabellar width, and fixigena ∼65% glabellar width. Thorax with eight segments. Pygidium rectangular, five pairs of spines, and moderately long pygidial spines.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho

Description.—Cranidium (N = 20) 1.9–7.6 mm long; rectangular, excluding posterior portion of fixigena, length 61 ± 3% width; high convexity (sag. and trans.); anterior margin evenly curved, width 64 ± 4% cranidial width; posterior margin, excluding occipital ring, nearly straight, posterior area of fixigena bowed posteriorly. Facial suture's anterior branch strongly divergent, 70 ± 4° to exsagittal line; posterior branch very strongly divergent, 98 ± 5° posteriorly to exsagittal line. Glabellar length 85 ± 2% and width 38 ± 3% cranidial length; width 23 ± 1% cranidial width; expanding anteriorly, width at frontal lobe 125 ± 9% glabellar width (K₂); moderate convexity (sag. and trans.); frontal lobe rounded, sometimes with slight medial sulcus. Axial furrows moderately deep, deeper adjacent to L2, shallow with intersection of eye ridge; preglabellar furrow shallow; lateral glabellar furrows moderately deep, S1 directed posterolaterally furrows, sometimes bifurcated, S2 commonly developed as pit isolated from the axial furrow in medium to larger specimens, S3 directed anteriolaterally, shallow isolated from axial furrows in larger specimens, S4 directed anteriolaterally, shallow. Occipital ring length 21 ± 2% glabellar length, slightly elevated above glabella, moderate convexity (sag. and tr.); short occipital spine; S0 curved slightly anteriorly and moderately deep adjacent to axial furrows, shallower medially, extending to axial furrow; posterior margin moderately curved. Frontal area length 15 ± 2% cranidial length. Anterior border concave, upturned, uniform length, moderately and evenly curved. Anterior border furrow evenly curved, very shallow, shallower than axial furrows. Very faint plectrum present extending from the junction of the ocular ridges and the glabella to the anterior lateral margin of cranidium. Fixigena width 64 ± 8% glabellar width (K2), low convexity, level. Palpebral lobe narrow, width 15 ± 3% lobe length; long, 60 ± 3% glabellar length; anterior about opposite L4, 24 ± 3% glabellar length behind anterior margin; moderate curvature; palpebral furrow moderate strength, broad. Ocular ridge absent. Posterior area of fixigena length 8 ± 1% glabellar length; width 71 ± 4% glabellar length; rounded termination with long fixigenal spine. Posterior border moderate convexity, slightly expanding distally; border furrow moderately deep, deepening and expanding distally, curved slightly posterolaterally.

Librigenae with spine 5.3–9.7 mm long (N = 5); wide, width 64 ± 7% length without spine; lateral margin moderately curved. Genal field slightly convex, width 46 ± 3% librigenal width. Border width 22 ± 2% librigenal width; flat, level; lateral border furrow moderately deep, shallowing towards posterior facial suture; posterior border furrow shallow, broad, very short. Anterior facial suture cuts nearly laterally across the anterior edge of librigenae. Genal spine slightly advanced, nearly flat in cross-section, long, length ranging ∼60–110% librigenal length.

Eight thoracic segments decreasing in width posteriorly. Axial furrows well defined. Thoracic pleura moderately wide, length (trans) ∼100% of axial width; anterior pleural band expanding distally, distal end forming long, flat, posterolaterally directed spine; posterior pleural band narrows distally, relatively low relief, persisting into pleural spine. Pleural spines directed posterolaterally, becoming posteriorly near pygidium.

Pygidium 1.4–3.7 mm long (N = 12); subrectangular, length 53 ± 3% width; anterior margin curved posterolaterally approximately half way to anterolateral corners; anterolateral corners rounded, adjacent to anterior portion of axis; five pairs of spines; projected posteriorly, decreasing is size posteriorly, spines terminate behind the posterior margin at nearly the same distance, enhancing the pygidial rectangular outline; moderately convex (sag.). Axis tapered, midwidth (AW2) 77 ± 4% axial width (AW1), anterior width 40 ± 3% pygidial width; length 77 ± 4% pygidial length; three axial rings, moderately convex; terminal axial piece moderate size, rounded; axial ring furrows moderate strength. Pleural furrows and bands curved posterolaterally to posterior at back end, moderately to weakly developed from anterior to posterior. Border weakly defined by change in slope of pygidial spines.

Exoskeleton thin; generally smooth on all external and internal surfaces, except fine granular surface on some specimens (Fig. 21.11).

Remarks.—The cranidium of Z. sampsoni has a thin, long posterior area of the fixigenae and posterior border that is, in part, underneath the palpebral lobe and slopes downward (Fig. 21.12, 21.13). This makes it difficult to prepare specimens without damage to the palpebral lobe and/or the posterior area of the fixigena (Fig. 21.10). As a result, only a few specimens (N = 10) were able to be used for comparison of cranidial width to other features. The pygidium has five pairs of marginal spines; however, the articulating ring of the second axial ring is visible in some specimens (Fig. 21.23, 21.24, 21.27, 21.30, arrows). This suggests that the anterior-most section is incompletely fused. This feature occurs in pygidia of different sizes (Fig. 21.23 versus 21.27) and suggests that it is not related to ontogeny.

Zacanthoides sampsoni is most similar to Z. divergensis Rasetti, 1951 (s.l.) in their strongly divergent anterior facial suture and rectangular pygidium, which distinguishes these species from other representatives of Zacanthoides. The two species differ in the former having less-divergent anterior facial sutures (∼70° versus 90° to an exsagittal line) and lacking a plectrum, and five pygidial spines. Also mentioned is the presence of a granular surface (Sundberg, 1994, p. 48), however, some specimens of Z. sampsoni do have fine granular surface (Fig. 21.11). In addition, Z. sampsoni has eight thoracic segments (versus nine), slightly more expanded glabella (125 ± 9% versus 105–115%), slightly wider fixigena (64 ± 8% versus 45–60% glabellar width), and longer pygidial spines.

Remarks.—The middle Cambrian ptychopariids have been a taxonomic mess due to different authors giving priority to different morphological features or just assigning taxa to the suborder level. Assigning a specimen or a species to a genus has been difficult, particularly when specimens are commonly disarticulated, exfoliated, fragmented, ontogenetic changes have not been established, and/or compressed in shale. A landmark and semi-landmark study can help establish the amount of variation in a species due to compression, slight tectonic distortion, ontogeny, and natural variation. In this study, PCA and 16 landmarks (Table 1) are used to help establish the generic placement of Resser's species. The landmarks were selected to represent cranidial features considered to be taxonomically important.

Type species.—Ptychoparia piochensis Walcott, 1886, from the Chisholm Shale, Pioche Hills, Nevada.

Diagnosis.—Cranidia subrectangular to subpentagonal with moderate sagittal convexity. Glabella moderately elongated, ranging from 55–65% of cranidial length, strongly tapered from S0 to S2 then less tapered, lateral glabellar furrows bifurcated, deepest laterally, shallow to very shallow medially; axial furrows deepest posteriorly, preglabellar furrow shallow. S0 moderately shallow to medially obscure. Anterior border slightly tapered distally, no medial inbend, anterior border furrow moderately shallow laterally to shallow medially. Fixigena with intraocular region moderately to wide from 50–75% glabellar width, slightly convex, level; anterior region moderately downsloping. Palpebral lobes relatively long, anterior set adjacent to S3 extending to or posterior of S1, moderately curved. Posterior area of fixigena strap-like with sharp termination, border widens distally; border furrow extends to suture. Anterior branches of facial sutures slightly to strongly divergent to anterior border; posterior branches strongly divergent to posterior border furrow, then nearly parallel. Librigena with wide genal area, spine moderate to long, flattened with shallow furrow extending into spine, broad-based. Thorax multisegmented, segments tapering posterior with moderate length pleural spines that become more posterolaterally directed posteriorly; fulcrum weakly developed. Pygidium suboval, micropygous; axis with one to three axial rings; poorly developed anterior pleural band; anterolateral corners rounded, opposite to the axis midlength; posterior margin with weak median notch arched in posterior view; doublure absent behind axis.

Remarks.—The diagnosis has been modified from Sundberg and McCollum (2000) to encompass the taxa from the Lakeview Limestone.

Discussion of type species.—The type material of Amecephalus piochensis (Walcott, 1886) was probably collected from mine dumps at the Half Moon Mine area near Pioche, Nevada. Walcott (1886) assigned a several specimens (USNM 15434) as syntypes (Fig. 22) and these may represent either three different species (Amecephalus piochensis, Alokistocare packi Resser, 1935, and Piochaspis sellata Levi-Setti, 1993) or one morphologically variable species. Resser (1935) assigned (USNM 90171, a–c, originally part of 15434; Fig. 22.1–22.5) to Alokistocare packi, but did not figure them. He also assigned a lectotype and paratypes (USNM 15434b) for Am. piochensis. Palmer (1954, pl. 16, fig. 5; Walcott, 1925 listed this specimen as 15434a and from USNM loc. 31) assigned the larger specimen as the holotype [lectotype] and reassigned Al. packi to Al. piochensis. Levi-Setti (1993) erected Piochaspis sellata, which is derived from the same locality as Walcott's specimens. Walcott (1925, pl. 15, fig. 10) figured an additional cranidium USNM 15434c, but it was not found in the type collection. In addition, the hypostome illustrated by Walcott (1886, pl. 28, fig. 1e) was not found in the type collection.

The lectotype assigned by Resser (USMN 15434b) is a nearly complete shield, part/counterpart that Walcott (1924, pl. 9, fig. 1) illustrated in naming the genus Amecephalus (Foster, 2011, fig. 10.1; Fig. 22.6, 22.7). The type collection has only one specimen (part/counterpart) labeled directly on the shale sample with ink as 15434b. This specimen, which was not illustrated by Palmer (1954), has a moderately long (sag.) and wide (trans.) anterior border, moderately wide (trans.) fixigena, long palpebral lobes, moderately long librigenal spine and an oval pygidium with faint pleural and interpleural furrows. Walcott (1886, pl. 26, fig. 2b; Fig. 22.9) also illustrated an isolated librigena (USNM 15434d) with a moderately long genal spine similar to the lectotype USNM 15434b.

The lectotype assigned by Palmer (USNM 15434a from USNM loc. 31 of Walcott, 1925; Fig. 22.10) has been illustrated by Walcott (1886, pl. 28, fig. 1; 1925, pl. 15, fig. 8) and Palmer (1954, pl. 16, fig. 5); however, this lectotype designation is invalid due to a prior designation by Resser (1935; ICZN Article 74.11; see International Commission on Zoological Nomenclature, 1999). This large cranidium has a broad anterior border, relatively short glabella, strongly curved S0 to S2 glabellar furrows, and extremely faint medial occipital furrow. These features separate this specimen from most of the other type specimens of Am. piochensis and differ from the lectotype in having a longer (sag.) and wider (trans.) anterior border, wider (trans.) fixigena and shorter palpebral lobes. USNM 15434c (Walcott, 1886, pl. 28, fig. 1a; Palmer, 1954, pl. 16, fig. 2; Fig. 22.8, 22.11), which is a nearly complete specimen lacking librigenae, shares those four features with the USNM 15434a, but is only half the size. The pygidium of this specimen is rectangular shape and has pleural and interpleural furrows, and laterally defined border.

One of Walcott's specimens (1886, pl. 28, fig. 1d; Foster, 2011, fig. 10.3; Fig. 22.1, USNM 90171a), which was assigned to Al. packi by Resser (1935) and Foster (2011), is identical to Piochaspis sellata (Levi-Setti, 1993, pl. 99) in its indentation of the anterior border into the preglabellar area, narrow intergenal area of the fixigena, relatively broad (trans.) width of the thoracic axial rings relative to the pleural lobes, thoracic pleural spines directed laterally to slightly posterolaterally, and librigenal spines short, pointed, directed ∼45° to the posterior lateral and narrowed based.

The holotype specimen assigned to Al. packi by Resser (1935; Walcott, 1886, pl. 28, fig. 1c; Palmer, 1954, pl. 16, fig. 1, Foster, 2011, fig. 10.2; Fig. 22.4, 22.5;) is similar to P. sellata, but differs from this species in lacking a pronounced median inbend of the anterior border, relatively narrower width of the thoracic axial rings relative to the pleural lobes, librigenal spines longer, pointed, directed posteriorly, adjacent to the pleural lobes and broad based. Resser (1935) stated that there was only the holotype and a paratype, but four specimens are present in the type collection.

Palmer (1954) did not list two of Walcott's specimens (1886, pl. 26, fig. 2?, 2a?; Fig. 22.2, 22.3) as belonging to Al. piochensis. It is unclear if specimen USNM 90171b (Fig. 22.2) is the same as that figured by Walcott because the left palpebral lobe and adjacent fixigenae are missing, unlike the illustration in Walcott (1886). This specimen and USNM 90171c (Fig. 22.3) are on the same shale slab oriented nearly at 90° to each other and illustrate tectonic distortion. These two specimens and an additional three specimens on the same slab do not illustrate an indentation of the anterior border and have wider anterior borders and intraocular region of the fixigena. It should be noted that the specimens are in dark green shale, as opposed to the typical brown shales containing the other type material that is not tectonically distorted. Walcott (1886, p. 34) did note that Ptychoparia piochensis occurs in two different levels (7 and 21) more than 1055 ft (320 m) apart. The lower report is only 96 ft (29 m) above Olenellus gilberti Meek in White, 1874, and this green slab could be from this locality.

Additional specimens in the type collection include a small pygidium (Fig. 22.12; not illustrated by Walcott, 1886) with same general features as USNM 15434e (Fig. 22.11), but more poorly preserved and several cranidia of the same general type (Fig. 22.13; not illustrated by Walcott, 1886) as in USNM 15434b (Fig. 22.6, 22.7).

In addition, Pack (1906) reported taxa from the shales near Half Moon Mine (Chisholm Shale), which included Ptychoparia piochensis and Ptychoparia kempi Pack, 1906. Pack stated that all the material is in the collections at Columbia University Museum under the catalog numbers 20018–20021 (P. piochensis) and 20023 (P. kempi). All illustrations in Pack are drawings, which lack the detail to determine what species they may be. Specimens in plate 2, figures 4, 4a, and 4b may belong to Al. packi. The hypostome illustrated in figure 4c belongs to a corynexochid. The single specimen of P. kempi in plate 3, fig. 1, is clearly the same as the lectotype of P. piochensis.

Discussion of Lakeview Limestone species.—Resser (1938a) identified six species of “Alokistocare” from the Lakeview Limestone. Alokistocare normale (pl. 1, fig. 44) was stated (p. 7) to be “much like A. subcoronatum except for its larger size. Also the furrows, eyelines, and distribution of relief in the brim are different.” Alokistocare noduliferum (pl. 1, figs. 52, 54) was stated (p. 7) to have “a wide brim, the test is finely and coarsely granulated, the brim is striated beneath the test, and two nodes are situated in the dorsal furrow a short distance forward of the occipital furrow.” Alokistocare natale (pl. 1, fig. 53) is differentiated from Al. noduliferum in (p. 7) “the surface … is finely granulated, has, in addition scattered larger granules.” Alokistocare nactum (pl. 1, fig. 41, 42) (p. 7) “is characterized by a medium brim, on which a rather wide flat brim is differentiated by its upturned position.” Alokistocare nothum (pl. 1, fig. 51, 55) is compared to Al. nactum, but has (p. 7) “A medium swelling causes the rim to be less even in width throughout.” Alokistocare notatus (Resser, 1938a, pl. 1, fig. 43) is stated (p. 8) to have higher convexity and “test is finely granulated, and only a narrow rim is differentiated by the upturned edge.”

One of the obvious differences between Resser's species is the size of the specimens, with Al. noduliferum and Al. notatus based on larger specimens (glabellar length >10.0 mm); Al. normale and Al. nactum based on medium-sized specimens (glabellar length 6.0–8.0 mm); and Al. natale and Al. nothum based on a small specimens (glabellar length 2.0–4.0 mm). At present, three species can be recognized and assigned to Amecephalus: (1) Am. noduliferus (including Al. natale) based on the bacculae next to the base of the glabella and fine granular ornamentation; (2) Am. notatus (including Al. nothum) based on the well-developed false anterior furrow, relatively narrow anterior border and coarse granular ornamentation; and (3) Am. normale (including Al. nactum) based on the very poorly developed false anterior furrow, relatively long (sag.) anterior border, no bacculae, and fine granular ornamentation. With the exception of the bacculae, the smaller specimens (< 4.0 mm) of the last two groups are difficult to distinguish, in part due to the exfoliation of the exoskeleton and the difficulty of removing the exoskeleton from the internal mold. The adherence of the exoskeleton to the exterior mold is the result of its external granular surface and a thin layer of spar calcite that forms on the internal portion of the sclerite that provides a parting surface. Some species of Amecephalus have a frontal area that contains an anterior false border furrow and a posterior true anterior furrow. This term was defined and justified by Fortey and Ruston (1976, p. 337).

PCA plots (Fig. 23) illustrate a considerable overlap in cranidial measures in smaller specimens of Am. notatus and Am. normale. Amecephalus noduliferus occupies a separate morphospace, if size is ignored (PC1). The two specimens of “Al.” nothum overlaps with Am. normale and the two specimens of “Al.” nactum occur in separate morphospace between Am. notatus and Am. noduliferus.

1938a Alokistocare normale Resser, p. 7, pl. 1, fig. 44.

1938a Alokistocare nactum Resser, p. 7, pl. 1, figs. 41, 42.

1939a Alokistocare idahoense Resser, p. 16, pl. 4, figs. 8, 9.

1939a Alokistocare spencense Resser, p. 16, pl. 4, figs. 10, 11.

1981 Alokistocare idahoense; Gunther and Gunther, p. 17, pl. 3, figs. A–C.

2015 Amecephalus idahoense; Robison et al., fig. 61.

Holotype.—Cranidium USNM 95028 from USNM loc. 37n.

Diagnosis.—Cranidium subtrapezoidal, moderate length frontal area (36 ± 3% cranidial length), nearly parallel anterior facial sutures, anterior border moderately wide (width 61 ± 7% cranidial width) and narrow (length 16 ± 2% cranidial length), false anterior furrow absent; genal caeca well developed on preglabellar field; palpebral lobes dorsally arched; fixigena slightly convex, gently sloping upwards; bacculae absent. Librigenae with genal caeca; genal spine relatively short (length ∼60% librigenal length), broad based with shallow lateral border furrow extending into spine. Pygidia nearly effaced, faint border furrow and anterior pleural furrow, anterior lateral corners located at the level of the posterior axial lobe, anterior margin strongly curved posterolaterally approximately 1/3 distance from axial lobe. Cranidium and librigena covered in fine granular ornamentation.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Spence Shale (Glossopleura walcotti Zone), Wasatch Mountains and Wellsville Mountains, Utah (Resser, 1939a; Campbell, 1974; Robison et al., 2015).

Description.—Cranidium 6.9 ± 3.4 mm long (N = 35); subtrapezoidal; anterior border width 61 ± 7% cranidial width, cranidial length 65 ± 7% cranidial width; moderate convexity (sag. and trans.); anterior margin evenly curved to slightly uneven, slightly arched dorsally; posterior margin, excluding occipital ring, distally curved posterolaterally. Anterior branches of facial sutures nearly parallel to anterior border; strongly convergent across anterior border; posterior branches strongly divergent. Glabella moderately elongated, length 63 ± 3% cranidial length; width 33 ± 2% cranidial width, moderately tapered, width at anterior end 64 ± 6% glabellar width; moderate convexity (sag. and trans.); frontal lobe rounded; length 63 ± 3% cranidial length; width 33 ± 2% cranidial width. Axial furrow moderately deep, slightly deeper posteriorly, slightly constricted at L2; preglabellar furrow moderately shallow. Lateral glabellar furrows moderate to shallow, S1 bifurcated posterior branch directed to center of occipital furrow; S2–S4 not bifurcated directed laterally to slightly anterior, S4 very faint or absent. Occipital ring slightly elevated above glabella, moderate convexity; small occipital node; length 20 ± 3% glabellar length; posterior margin convex posteriorly, slightly curved medially. S0 gently curved anteriorly, moderately deep, and lateral portions arched anteriorly and deeper. Bacculae absent. Frontal area nearly equally divided; length 36 ± 3% cranidial length. Preglabellar field slightly convex, moderately downsloping, length 55 ± 5% frontal area length. Anterior border nearly flat and level, stronger curve medially, straighter laterally, slightly tapering laterally, length 16 ± 2% cranidial length. Anterior border furrow shallow, shallower medially, shallower than axial furrows; false anterior furrow absent. Fixigena slightly convex, gently sloping upwards, anterior area slightly downsloping; width 56 ± 5% glabellar width. Palpebral lobes moderately curved, sloping up, narrow, moderately long, length 46 ± 4% glabellar length; anterior margin located opposite L4. Ocular ridge moderate strength, very faint double band in larger specimens, slightly curved, directed moderately posterolaterally from glabella at 75 ± 3° to axis. Posterior area of fixigena strap like, sharp, nearly 90° termination; length (exsag.) 28 ± 3% glabellar length; width 82 ± 11% glabella length.

Librigenae 1.9–10.3 mm long excluding spine (N = 5); wide, width 51 ± 5% length without spine; lateral margin moderately curved. Genal field moderately convex. Border slightly convex, wider posteriorly, width ∼22 ± 5% librigenal width; border furrows moderate, shallower posterior and extending down into spine. Librigenal spine moderately long, 45–60% librigenal length (N = 2), slightly curved, flattened.

Rostral plate and hypostome unknown.

Thorax with at least 21 segments, tapering towards very small pygidium (pygidial width ∼25% cranidial width). Pleural segments wider than axial ring, directed laterally, directed moderately posterolaterally at moderately developed fulcrum. Anterior and posterior pleural bands strongly convex and uniform in length. Interpleural furrow deep and narrow to fulcrum, then shallowing. Pleural spine moderately short length, termination sharp.

Pygidium 0.9–1.57 mm long (N = 4); nearly oval to aleate, length 40 ± 4% width; margin smooth, anterior margin curved posterolaterally approximately half way to anterolateral corners; anterolateral corners moderately rounded, adjacent to anterior portion of axis; posteromedial notch present(?); moderately convex (sag.). Axis anterior width 37 ± 3% pygidial width; length 89 ± 5% pygidial length; postaxial ridge absent; slightly tapered, medial width 89 ± 5% anterior width, three axial rings, moderately convex; terminal axial piece moderate size(?), rounded; axial ring furrows nearly effaced in smaller specimens. Pleural regions moderately curved laterally; pleural furrows and bands poorly developed except anterior pair. Border weakly defined; border furrow very shallow anteriorly.

Exoskeleton with a fine granular surface; preglabellar area and genal area of librigenae covered with genal caeca.

Remarks.—Amecephalus normale ranges in cranidial length from 2.1–15.1 mm (Fig. 26.1). With this range in size, there are some significant changes in morphology due to ontogeny, which include a decrease in cranidial length to width from 75% to 55% (R² = 0.60; Fig. 26.2) and anterior cranidial width to posterior cranidial width from 70% to 55% (R² = 0.44; Fig. 26.3). Other decreases, but much less constrained, are glabellar length to cranidial length (64% to 62%, R² = 0.05); glabellar anterior with to basal glabellar width (67% to 57%, R² = 0.19); palpebral lobe length to glabellar length (47% to 42%, R² = 0.25); and anterior border width to frontal area width (48% to 40%, R² = 0.16). The ratio of glabellar width to length increases with cranidial size (70% to 90%, R2 = 0.60, Fig. 26.4).

Alokistocare nactum Resser, 1938a is included within the species, given their similarity to smaller specimens of Am. normale (Figs. 23, 24.3, 24.4, 26).

PCA of the specimens assigned to Am. normale and Am. notatus illustrate that the two taxa occupy distinct morphospaces, but overlap occurs in relatively smaller specimens (Fig. 23). Samples from the Lakeview Limestone were assigned to one or the other species based on (1) fine or coarse granules, and/or (2) presence or absence of the false anterior furrow. However, the common exfoliation of specimens makes it difficult to determine if a specimen has either fine or coarse granules, and the false anterior furrow absent is poorly developed in smaller specimens (the relatively thick exoskeleton hampers the effort to identify the false anterior furrow as absent).

In many aspects, Am. normale is similar to specimens of Am. piochensis (Walcott, 1886), re-illustrated by Palmer (1954, pl. 16, figs. 1, 2, 5; Fig. 22.4, 22.8). The two smaller paratypes (cranidial lengths of 14.1 mm and 6.5 mm) illustrated by Palmer and additional material collected by the author (Fig. 27) are similar in: glabella shape and convexity; frontal area construction with a medially upturned anterior border; intraocular fixigenae sloping upwards, slightly convex and of similar width; palpebral lobes tilted upwards; posterior portion of the fixigena down sloping and bluntly terminated; librigenae with moderately long, broad base spine and a border furrow extending into spine; thoracic segments with relatively short pleural spines; and pygidia with a relatively short transverse width. Differences are relatively minor and Am. piochensis has a slightly coarser granulation (Fig. 25.6), slightly wider anterior border (trans.), and slightly narrower posterior margin width (trans.). The difference in transverse widths is illustrated by comparing 16 landmarks between the two species (Fig. 28). The differences between Am. piochensis and Am. normale are, in the former: a very slightly more constricted glabella margin (Fig. 28.2, landmarks 6–12; sagittal landmarks 1–5 are about the same); and the larger differences in the abaxial landmarks (13–15) are occurring outward. This essentially creates a stronger curvature of the anterior border, wider anterior border, shorter anterior facial suture between the anterior border furrow and the anterior end of the palpebral lobes, and overall widening of the anterior half of the cranidium. Principal component analysis on the landmarks indicates that the distribution of the two taxa is different (Fig. 28.3, 28.4).

These significant differences may be the result of compaction given that Am. normale is preserved in limestone and Am. piochensis and Am. idahoense are preserved flattened in shale. Figure 28.2 illustrates that generally movement of landmarks are inwards in the posterior portion of the cranidium and outwards in the anterior portion. Distribution of cracks on specimens of Am. piochensis (Fig. 29) is concentrated in the center of the frontal area, center of the occipital ring, at the anterior end of the palpebral lobes, at the junction of the posterior area of the fixigena and occipital ring, and posterior from the palpebral lobe to the posterior margin. The cracks in the frontal area could easily expand the transverse width, but it is unknown if other cracks would shorten the transverse widths from the anterior margin of the palpebral lobes to the posterior margin of the cranidium. Although these similarities and compressional changes would suggest a synonymy of the two species, a complication arises when the lectotype of Am. piochensis (Palmer, 1954, pl. 16, fig. 5) is considered as discussed above.

Resser (1939a) proposed five new species of Alokistocare from the Spence Shale of Idaho: Al. septum, Al. idahoense, Al. spencense, Al. laticaudum, and Al. puncatum. Of these, Al. idahoense and Al. spencense are considered as junior synonyms of Am. normale from the Lakeview Limestone. Amecephalus idahoense illustrated by Robison et al. (2015, fig. 61) have identical glabellar, librigenae, and pygidial features to Am. normale.

Amecephalus althea (Walcott, 1916a) from the Bright Angel Formation (McKee and Resser, 1945; Foster, 2011) and Am. normale are similar in both having a relatively narrow fixigena and relatively wide and long palpebral lobes, but differ in the former having a triangular frontal area swelling and very long fixigenal spines.

1938a Alokistocare noduliferum Resser, p. 7, pl. 1, figs. 52, 54.

1938a Alokistocare natale Resser, p. 7, pl. 1, fig. 53.

2015 Amecephalus laticaudum (Resser, 1939a); Robison et al., fig. 63.

Holotype.—Cranidium USNM 95029 from USNM loc. 37n.

Paratype.—Cranidium USNM 95029a from USNM loc. 37n.

Diagnosis.—Cranidium subsquare, with long frontal area (45 ± 1% cranidial length), divergent anterior facial sutures, anterior border transversely wide (width 93 ± 8% cranidial width) and sagittally narrow (length 22 ± 2% cranidial length), false anterior furrow present; genal cecea well developed on preglabellar field; palpebral lobes dorsally arched; fixigena flat, gently sloping upwards; bacculae present. Librigenae with genal caeca; genal spine relatively long (length ∼100% librigenal length), broad based with deep lateral border furrow extending into spine. Pygidia nearly effaced, faint border furrow and anterior pleural furrows, anterior lateral corners located at the level of the posterior axial lobe, anterior margin strongly curved posterolaterally approximately 1/3 distance from axial lobe. Cranidium and librigena covered in fine granular ornamentation.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho. Spence Shale (Glossopleura walcotti Zone), Wellsville Mountains, Utah (Robison et al., 2015).

Description.—Cranidium 11.8 ± 6.8 mm long (N = 6); subsquare, anterior border width 93 ± 8% cranidial width, cranidial length 78 ± 3% cranidial width; moderate convexity (sag. and trans.); anterior margin evenly curved, very slightly arched dorsally; posterior margin, excluding occipital ring, distally curved posterolaterally. Anterior branches of facial sutures divergent to anterior border; moderately then strongly convergent across anterior border; posterior branches moderately divergent. Glabella moderately short, length 55 ± 2% cranidial length; width 35 ± 3% cranidial width, moderately low convexity (sag. and trans.); moderately tapered, width at anterior end 65 ± 5% glabellar width; frontal lobe broadly rounded to nearly flat medially. Axial furrow moderately shallow, slightly deeper anteriorly, slightly constricted as S3; preglabellar furrow moderately deep. Lateral glabellar furrows moderate to shallow depth, S1 bifurcated with posterior branch directed towards center of occipital furrow; S2–S4 not bifurcated directed laterally to slightly anterior, S4 very faint or absent. Occipital ring slightly elevated above glabella, moderate convexity; small occipital node; length 17 ± 2% glabellar length; posterior margin convex posteriorly, slightly curved medially. S0 gently curved anteriorly, moderately deep and lateral portions arched anteriorly and deeper. Bacculae present adjacent to L1. Frontal area equally divided; length 45 ± 1% cranidial length. Preglabellar field slightly convex, moderately downsloping, length 51 ± 5% frontal area length. Anterior border nearly slightly concave and level, uniformly curved, uniform length, length 22 ± 2% cranidial length. Anterior border furrow very shallow, uniform depth, shallower than axial furrows; false anterior furrow present, less obvious in larger specimens. Fixigena nearly flat, gently sloping upwards, anterior area strongly downsloping laterally; width 68 ± 9% glabellar width. Palpebral lobes moderately curved, slightly sloping up, narrow, moderately long, length 40 ± 4% glabellar length; anterior margin located opposite L4. Ocular ridge moderate strength, double band absent, slightly curved, directed moderately posterolaterally from glabella at 74 ± 2° to axis. Posterior area of fixigena triangular, sharp, nearly 45° termination; length 38 ± 9% (exsag.) glabellar length; width 78 ± 5% glabella length.

Librigenae 4.1–12.9 mm long excluding spine (N = 2); wide, width ∼45% length without spine; lateral margin moderately curved. Genal field moderately convex. Border concave, wider posteriorly, width ∼40% librigenal width; border furrows shallow, deeper posteriorly, and extending down into spine. Librigenal spine long, ∼100% librigenal length, slightly curved, flattened.

Rostral plate and hypostome unknown.

Thorax with unknown number of segments. Pleural segments wider than axial ring, directed laterally, directed moderately posterolaterally at moderately developed fulcrum. Anterior and posterior pleural bands strongly convex and uniform in length. Interpleural furrow deep and moderately to fulcrum, then narrowing. Pleural spine moderately short length, termination sharp.

Pygidium 2.7–4.6 mm long (N = 2); subrectangular, length ∼70% width; margin smooth, anterior margin slightly curved posterolaterally, approximately half way to anterolateral corners then strongly directed posterolaterally; anterolateral corners moderately rounded, adjacent to posterior portion of axis; posteromedial notch present, slight; moderately convex (sag.). Axis anterior width ∼30% pygidial width; length ∼85% pygidial length; postaxial ridge absent; slightly tapered, medial width ∼85% anterior width, three axial rings, moderately convex; terminal axial piece moderate size, rounded. Pleural regions moderately curved laterally; pleural furrows and bands poorly developed, except anterior pair. Border weakly defined; border furrow very shallow anteriorly.

Exoskeleton with a fine granular surface; preglabellar area and genal area of librigenae covered with genal caeca.

Remarks.—Resser (1938a) diagnosed this species with the wide anterior border, finely granulated cranidium, genal caeca, and bacculae. Alokistocare natale has these same features and is placed into synonymy. This species is unique for the genus in its possession of bacculae. Amecephalus laticaudum illustrated by Robison et al. (2015, fig. 63 left) is identical to Am. noduliferus from the Lakeview Limestone having a truncated frontal lobe, broad frontal area (trans. and sag.), bacculae adjacent to the base of L1 of the glabella.

In many aspects, Am. noduliferus resembles Palmer's proposed lectotype of Am. piochensis with its wide anterior border (both trans. and sag.), glabellar shape, and sharper termination of the posterior portion of the fixigena, but the latter lacks the bacculae at the base of the glabella. In addition, the illustrated specimen of Am. piochensis by Levi-Setti (1993, pl. 98) from the type area illustrates the same cranidial features as Palmer's lectotype, including the lack of bacculae, but also the librigenal and pygidial features of Am. noduliferus.

Foster (2014, fig. 5.18C) assigned a similar looking specimen from the Half Moon Mine area to Amecephalus althea with its characteristic triangular swelling in the frontal area that separates this species from Am. noduliferus. However, this may indicate that four species of Amecephalus may occur at the type area of Am. piochensis.

1938a Alokistocare notatum Resser, p. 8, pl. 1, fig. 43.

1938a Alokistocare nothum Resser, p. 7, pl. 1, figs. 51, 55.

Holotype.—Cranidium USNM 95033 from USNM loc. 37n.

Diagnosis.—Cranidium subtrapezoidal, moderate length frontal area (37 ± 2% cranidial length), slightly divergent anterior facial sutures, anterior border moderately wide (width 72 ± 5% cranidial width) and narrow (length 17 ± 2% cranidial length), false anterior furrow present; genal caeca well developed on preglabellar field; palpebral lobes slightly sloping upwards; fixigena slightly convex, gently sloping upwards; bacculae absent; covered in moderately coarse granular ornamentation.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho.

Description.—Cranidium length 4.6 ± 1.0 mm long (N = 45); subtrapezoidal, anterior border width 72 ± 5% cranidial width, cranidial length 66 ± 4% cranidial width; moderate convexity (sag. and trans.); anterior margin evenly curved, slightly arched dorsally; posterior margin, excluding occipital ring, slightly curved posterolaterally. Anterior branches of facial sutures slightly divergent to anterior border; strongly convergent across anterior border; posterior branches strongly divergent. Glabella moderately elongated, length 63 ± 2% cranidial length; width 33 ± 2% cranidial width, moderately tapered, width at anterior end 65 ± 4% glabellar width; moderate convexity (sag. and trans.); frontal lobe rounded; length 63 ± 2% cranidial length; width 33 ± 2% cranidial width. Axial furrow moderately deep, slightly deeper posteriorly, slightly constricted at S3; preglabellar furrow moderately shallow. Lateral glabellar furrows moderately deep, S1 bifurcated, posterior branch directed to center of occipital furrow; S2–S4 not bifurcated, directed laterally to slightly anterior, S4 very faint or absent. Occipital ring slightly elevated above glabella, moderate convexity; small occipital node; length 20 ± 2% glabellar length; posterior margin convex posteriorly, slightly curved medially. S0 gently curves anteriorly, moderately deep and lateral portions arched anteriorly and deeper. Bacculae absent. Frontal area nearly equally divided; length 37 ± 2% cranidial length. Preglabellar field slightly convex, moderately downsloping, length 54 ± 8% frontal area length. Anterior border very slightly concave and level, uniform curvature, slightly tapering laterally, length 17 ± 2% cranidial length. Anterior border furrow shallow to moderately deep laterally; shallower than axial furrows; false anterior furrow well developed in larger specimens, fainter is smaller specimens, tapering laterally, absent at lateral margins of cranidium. Fixigena slightly convex, level, anterior area moderately downsloping; width 60 ± 5% glabellar width. Palpebral lobes moderately curved, slightly sloping up, narrow, moderately long, length 45 ± 3% glabellar length; anterior margin located opposite L3. Ocular ridge moderate strength, consists of two faint bands, slightly curved, directed moderately posterolaterally from glabella at 76 ± 4° to axis. Posterior area of fixigena strap like, sharp, nearly 90° termination; length 30 ± 3% glabellar length; width 79 ± 6% glabella length.

Cranidium with a moderately coarse granular surface; preglabellar area and genal area of fixigenae covered with genal caeca, strongly developed on internal molds.

Rostral plate, hypostome, librigena, thorax, and pygidium unknown.

Remarks.—Amecephalus notatus is only known from rare isolated cranidia. Pygidia and librigena found with this species do not contain the moderately coarse granular ornament and are here assigned to Am. normale.

“Alokistocare” nothum is placed in to Am. notatus and considered the same given their overall cranidial morphology, although the two type specimens plot slightly away from Am. notatus in the PCA (Fig. 23). Given that the two forms occur in the same horizon, this difference is not considered significant. The holotype of Amecephalus notatus is larger and better preserved than the two specimens of “Al.” nothum, even though the latter species was originally described a page before the former (ICZN Article 24.2, “First Reviser” can choose which species name to use as senior synonym regardless of the order of description within a paper; see International Commission on Zoological Nomenclature, 1999). Amecephalus notatus differs from Am. normale in having divergent anterior branches of the facial suture and a narrower (tr.) anterior border and fixigena. Resser diagnosed this species with a medium swelling in the anterior border that causes the border to be uneven in width.

Type species.—Conocephalites cordillerae Rominger, 1887, Stephen Formation, British Columbia, Canada.

Diagnosis.—Cranidium with a glabella with subparallel sides, shallow lateral glabellar furrows, S1 with a long and strongly backward directed branch, S2–S4 short and simple; palpebral lobes small, located anterior to the cranidium midlength, defined adaxially by a shallow and incompletely developed palpebral furrow; ocular ridges that curve distinctly backward; fixigenae gently convex, ≥ 50% wider (trans.) than glabellar width; convex anterior border wide (trans.); facial sutures with anterior branches subparallel close to the palpebral lobes and then convergent towards the anterior border, the posterior branches diverging ∼45° to exsagittal line. Librigenae with a rounded posterolateral corner or a short genal spine. Thorax composed of subequal segments with only small pleural spines. Pygidium small, sublenticular, with an entire, nearly uniformly curved posterior margin; axis relatively broad and long pygidial axis; pleurae without a consistent segmentation; border and border furrow obscure.

Remarks.—Geyer and Peel (2017, p. 272) provided an informal diagnosis of Elrathina and a review of Elrathina species. The above diagnosis is derived from this informal diagnosis (also see Sundberg, 2018).

1938a Elrathia idahoensis Resser, p. 8, pl. 1, figs. 36–40.

Holotype.—Cranidium USNM 95034 from USNM loc. 37n.

Paratypes.—Specimens USNM 95034a–e from USNM loc. 37n.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho.

Diagnosis.—Cranidium with subparallel to slightly tapering glabella (79 ± 5% glabellar width) with a rounded to slightly flattened front; palpebral lobes small (25 ± 3% glabellar length), but not minute, located medially on cranidium; ocular ridges with gentle curvature; anterior border moderately narrow (length 11 ± 2% cranidial length), without medial swelling; preglabellar field of relatively long (length 15 ± 2% cranidial length); librigenae with moderately short genal spine (30 ± 12% librigenal length); geniculation of thoracic pleurae abaxially to pleural mid-length; pygidium subtriangular, posteromedial notch moderately developed; pygidial axis broad (width 43 ± 5% pygidial width), with one to two rings, its posterior end rounded without slightly inflated bulbs, reaching almost to the posterior margin (length 90 ± 3% pygidial length); pygidial pleurae with one furrow.

Description.—Cranidium 5.1 ± 2.0 mm long (N = 31); subtrapezoidal, moderately low convexity (sag. and trans.); anterior margin slightly and evenly curved, slightly arched dorsally; posterior margin, excluding occipital ring, nearly straight, directed slightly posterolaterally. Anterior branches of facial sutures slightly convergent 17 ± 7° to anterior border, more convergent to anterior margin; posterior branches moderately divergent 53 ± 4°. Glabella moderately elongated, slightly tapered, width at anterior end 79 ± 5% glabellar width (K2); moderately convex (sag. and trans.); frontal lobe bluntly rounded; length 74 ± 3% cranidial length; width 33 ± 2% cranidial width. Axial furrows moderately deep, straight and convergent towards anterior; preglabellar furrow moderately shallow. Lateral glabellar furrows very shallow, S1 bifurcated directed posteriorly, S2 slightly posterior, S3 and S4 faint or absent. Occipital ring not elevated above glabella, moderately convex; moderate occipital spine; length 19 ± 2% glabellar length; posterior margin convex posteriorly, evenly curved. S0 straight to slightly curved anteriorly medially in larger specimens; and moderately deep, shallower medially. Frontal area subequally divided; length 25 ± 3% cranidial length. Preglabellar field very slightly convex, slightly downsloping, length 15 ± 2% cranidial length, 57 ± 6% frontal area length. Anterior border moderately convex, level, slightly tapering laterally, no medial inbend, length 11 ± 2% cranidial length. Anterior border furrow moderate width and shallow, shallower medially, shallower than axial furrows. Fixigena slightly convex, level, anterior area slightly downsloping, lateral portions more strongly downsloping; width 59 ± 6% glabellar width (K2). Palpebral lobes nearly straight, slightly upturned, moderately narrow and moderately short, length 25 ± 3% glabellar length; anterior margin located opposite frontal lobe. Ocular ridge faint to very faint, straight to slightly arched, directed slightly posterolaterally from glabella at 80 ± 3° to axis. Posterior area of fixigena triangular, terminated with rounded corner; length 72 ± 5% glabellar length; width 46 ± 3% glabella length.

Librigenae 4.8 ± 1.1 mm long (N = 6); moderately wide, width 34 ± 2% length without spine; lateral margin moderately curved. Genal field slightly convex. Border slightly convex, uniform in width, width 29 ± 5% librigenal width; border furrows shallow. Librigenal spine moderately short, 30 ± 12% librigenal length, nearly straight; shorter and slightly deflected laterally in smaller specimens.

Rostral plate and hypostome unknown.

Thorax with at least 17 segments, tapering towards small pygidium. Pleural segments nearly as wide as axial ring, directed laterally, directed moderately posterolaterally at moderately developed fulcrum. Anterior pleural band moderately convex and uniform in length, posterior band moderately convex and narrowing to fulcrum, then uniform length. Interpleural furrow moderately deep and widening to fulcrum, then narrowing. Pleural spine short, termination pointed to sharply rounded.

Pygidium 0.9–1.8 mm long (N = 6); subtriangular, length 40 ± 2% width; margin smooth, anterior margin distally slightly to moderately curved posterolaterally; anterolateral corners rounded, adjacent to anterior portion of axis; posteromedial notch moderately developed; moderately convex (sag.). Axis slightly tapered mid width 85 ± 6% anterior width, anterior width 45 ± 4% pygidial width; length 91 ± 3% pygidial length, postaxial ridge absent; one or two axial rings, moderately convex; terminal axial piece moderate size(?), rounded; axial ring furrows effaced. Pleural regions nearly flat, level; anterior pleural furrow wide and very shallow, extending to border(?); no additional pleural furrows. Border poorly defined, narrow, wider at anterolateral corners, level; absent at posterior margin; border furrow absent.

Faint, fine granules on glabella, occipital ring, librigenae, axial rings, and thoracic pleura. Faint genal caeca on preglabellar regions of larger specimens.

Remarks.—Resser (1938a, p. 8) characterized this common species by “a fullness of all parts of the cranidium…” due to the moderately convex nature of the glabella and anterior border. Elrathia idahoensis was re-assigned to Elrathina Walcott, 1924 by Robison (1964, p. 541), which is maintained here due to the nearly parallel sided glabella; anteriorly placed, small palpebral lobes; convergent anterior branches of the facial suture; and exsagittally long posterior area of the fixigena. This species also fits the concept of Elrathina (Geyer and Peel, 2017; Sundberg, 2018), except for the relatively long librigenal spine. Nearly all of the specimens have been compressed to some extent, which is evident from the fractures crossing the cranidia. In many instances, this compression could have reduced the convexity of the glabella and anterior border. Almost all specimens have an occipital node, with one specimen (Fig. 33.14–33.16) showing the recurved spine.

Small changes occur during the ontogeny of later meraspids (>1.5 mm) to holaspids. In general, cranidium becomes more rectangular, glabellar width to length ratio increases, and glabellar taper increases.

This species is similar to E. hera Geyer and Peel, 2017 in overall cranidial shape, but differs in the a longer preglabellar area and a wider (trans.) anterior border; librigenae with a slightly longer genal spine; and a pygidium with a broader (trans.) axis.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho.

Remarks.—The rare specimens assigned to this species are mostly small meraspids and are similar to the smaller meraspids of E. idahoensis. Differences between the two species are the former having a cranidium with a narrower (trans.) anterior border, shorter (sag.) preglabellar area; librigenae with very minute thorn like genal spine (Fig. 34.9, 34.10); and pygidia with better defined pleural, interpleural, and axial ring furrows. These specimens are placed into open nomenclature due to the lack of larger and additional specimens.

Geyer and Peel (2017, p. 272) pointed out that the figured specimens of E. spencei (Resser, 1939a) probably represent three different species, which is agreed to herein. The holotype of the species (Resser, 1939a, pl. 5, fig. 15) is very similar to E. cf. idahoensis, but differs from the latter in a more tapered glabella, similar to a single specimen of the latter (Fig. 34.7), and an indentation of the posterior pygidia margin. However, the indentation of the pygidium may be the result of compaction, which enhanced the arch of the posterior margin seen in the pygidia assigned to E. cf. idahoensis (Fig. 34.12, 34.13). Resser's material of the Spence Shale needs to be restudied to determine the morphological characters of Elrathina spencei and the similar Elrathia rara Resser, 1939a and Clappaspis lanata Resser, 1939a and determine their taxonomic affinity.

Type species.—Utia curio Walcott, 1924, from the Spence Shale, Bear River Range, Idaho, by original designation.

Diagnosis.—Cranidium subrectangular with strong sagittal convexity. Glabella moderately elongated ranging from 65–70% of cranidial length, subparallel, tapered from S0 to S2 then nearly parallel, lateral glabellar furrows shallow to very shallow medially; axial furrows deepest anteriorly, preglabellar furrow moderately deep. S0 moderately deep. Frontal area and adjacent portion of fixigena convex, level in posterior portion, anterior portion directed strongly dorsal. Anterior border slightly tapered distally, positioned nearly vertical, no medial inbend, anterior border furrow shallow laterally to very shallow medially. Fixigena with intraocular region wide from 75–80% glabellar width, slightly depressed to flat, level; anterior region moderately downsloping. Palpebral lobes moderately long at 40–50% glabellar length, anterior set adjacent to L3, extending to or posterior of S1, slightly curved. Posterior area of fixigena triangular with sharp termination, border uniform length (exsag.); border furrow deep, extends to suture. Anterior branches of facial sutures convergent to anterior border; posterior branches strongly divergent to posterior border furrow.

Remarks.—The diagnosis is based on Walcott (1925, p. 119–121), and features seen in Utia debra n. sp. Known mainly from cranidia, this genus is distinct with its strongly convexity of the frontal area where the anterior portion is nearly vertical. Yuknessaspis Rasetti, 1951 from the higher Ehmaniella Zone (Sundberg, 1994) are similar in the deep glabellar furrows and strongly convexity of the frontal area, but generally has a more tapered glabella, broadly rounded termination to the posterolateral portion of the fixigena, and more pronounced anterior border furrow.

1938a Utia curio; Resser, p. 9, pl. 1, figs. 19, 20 (not fig. 21 = Oryctocara).

1939a Utia curio; Resser, p. 21, pl. 2, fig. 3.

Holotype.—Cranidium USNM 724166 from USNM loc. 44280.

Paratypes.—USNM 95041 and 95041a (USNM loc. 37n) and 724161–724165 (USNM 44282), 724167–724170 (USNM 44279), 724171–724176 (USNM 44282).

Diagnosis.—Cranidium having a stronger curved anterior border, longer preglabellar area (sag. in dorsal view), flexure of preglabellar area to anterior border broadly rounded.

Occurrence.—Lakeview Limestone (Ptychagnostus praecurrens Zone), Pend Oreille Lake, Idaho (Resser, 1938a). Spence Shale (Glossopleura walcotti Zone), Antimony Canyon, Wellsville Mountains, Utah (Campbell, 1974).

Description.—Cranidium 5.15 ± 0.76 mm long (N = 7, without single 1.67 mm meraspid); subrectangular, strong convexity (sag. and trans.); anterior margin moderately and evenly curved, not arched dorsally; posterior margin, excluding occipital ring, curved posterolaterally. Anterior branches of facial sutures slightly convergent to anterior border, ∼20°, more convergent to anterior margin; posterior branches moderately divergent, ∼80°. Glabella moderate length, slightly tapered with slight constriction at S2 glabella furrows, width at anterior end 84 ± 4% glabellar width (K2); moderately low convexity (sag. and trans.); frontal lobe bluntly rounded with very slight medial sulcus; length 68 ± 3% cranidial length; width 32 ± 2% cranidial width. Axial furrows moderately deep, constricted at S2 and convergent towards anterior; preglabellar furrow moderately deep. Lateral glabellar furrows moderately shallow, S1 bifurcated directed posteriorly, S2 laterally, S3 laterally and sometimes isolated from axial furrow, and S4 faint, directed slightly anteriorly, sometimes isolated from axial furrow. Occipital ring not elevated above glabella, moderately convex; small node; length 15 ± 7% glabellar length; posterior margin nearly straight. S0 curved posteriorly then anteriorly medially; and moderately deep. Frontal area subequally divided; length 32 ± 3% cranidial length. Preglabellar field broadly convex, upsloping then strongly convex dorsally, length 93 ± 2% frontal area length. Anterior border moderately convex, laterally level, mostly vertical, tapering laterally, length 2 ± 1% cranidial length. Anterior border furrow narrow and moderately shallow, shallower medially, shallower than axial furrows. Fixigena nearly flat, very slightly depressed in intraocular regions, level, anterior area strongly downsloping, lateral portions more strongly downsloping; width 78 ± 3% glabellar width (K2). Palpebral lobes nearly straight, upturned, narrow and short, length 33 ± 2% glabellar length; anterior margin located opposite L3 lobe. Ocular ridge moderate, slightly arched, directed slightly posterolaterally from glabella at 77 ± 3° to axis, separated from glabella by axial furrows. Posterior area of fixigena triangular, terminated with acute corner; length 45 ± 5% glabellar length; width 81 ± 7% glabella length. Posterior boarder strongly convex, narrow, boarder furrow deep, broadens laterally.

Granules scattered on frontal area, fixigena, occipital ring, and top of glabella. Anterior border with terrace lines. Exfoliated surface of frontal area with genal caeca.

Librigenae, rostral plate, hypostome, thorax, and pygidium unknown.

Etymology.—Named for my wife, Debra, who has continuously supported me in my research on trilobites.

Remarks.—The types U. curio (Fig. 36) are mostly exfoliated, have a relatively thick exoskeleton, and are preserved in shale, but do not appear to be compressed. Utia curio? (Sundberg, 2018, p. 39–40, fig. 20.1–20.3) from the Emigrant Formation and from the Gordon Shale, Montana (Schwimmer, 1973), are here confirmed to belong to the species. Cranidium of U. debra n. sp. differ from U. curio in the latter having a slightly curved anterior border, a shorter preglabellar area in dorsal view, and a sharper flexure of the preglabellar area dorsally toward the anterior border. Campbell (1974) illustrated two additional specimens that can be assigned to U. debra n. sp. from the Glossopleura walcotti Zone, Spence Shale, Utah.

Nearly all the Lakeview Limestone specimens (Fig. 35) are mostly or completely exfoliated. Where the exoskeleton is preserved, fine granules cover the marginal fixigena and frontal area, but are reduced in the palpebral lobe area and absent on the glabella and terrace lines cross the anterior border. Small meraspids have granules covering the entire cranidium. Prominent to faint genal caeca cross the frontal area on exfoliated specimens, but is not seen on the dorsal surface.

Remarks.—Ptychoparioid hypostomes were found, but their generic affiliation cannot be assessed.