Type species.—Orthoceras knoxensis McChesney, 1859.

Orthoceras knoxensis [sic] McChesney, 1859, p. 69.

Pseudorthoceras knoxense (McChesney). Girty, 1911, p. 143; Sturgeon et al., 1997, p. 23, pl. 1–3, figs. 1–21 [with earlier synonymy]; Kröger and Mapes, 2004, p. 562, figs. 1.7, 4, 5.9, 6.7, 6.15 [with additional synonymy].

Description.—Two fragmentary specimens including an apical shell and a deformed more adoral phragmocone are available for this study; they are longiconic orthocones; embryonic shell exhibits faint endogastric curvature; except for vicinity of apex that has very weak longitudinal lirae, shell surface lacks ornamentation. Sutures directly transverse; camerae short; dorsoventral section prepared from adoral shell shows siphuncular structure of cyrtochoanitic septal necks and strongly inflated ventral connecting rings; dorsal part of the larger specimen is mostly crushed. Endosiphuncular deposits form continuous lining on ventral siphuncular wall; cameral deposits differentiated into episeptal-mural and hyposeptal.

Material examined.—AMNH 5892, 5893.

Discussion.—Numerous specimens exhibiting wide morphological variations have been assigned to Pseudorthoceras knoxense, whose stratigraphic range is exceptionally long, with a range spanning the Chesterian (Late Mississippian, early Carboniferous; Kröger and Mapes, 2004) to Wordian (middle Permian; Gordon, 1964).

Pseudorthoceras knoxense was first recorded by Smith (1938, p. 5, 6, pl. 1, figs. 10–12) from the Buckhorn Asphalt Lagerstätte. Characters of the present specimens also fall within the morphologic range of P. knoxense accepted by previous workers. However, direct comparison between them and the syntypes from the Pennsylvanian McLeansboro Group of Illinois is difficult, because the original description by McChesney (1859) is too simple to clarify their details and his publication lacks illustrations. There is a possibility that this taxon contains several not yet described species or subspecies. This would require reexamination of the types and revision of the specific diagnosis.

Type species.—Orthoceras tricamerae Smith, 1938, by monotypy.

Diagnosis.—Conchs longiconic with weak exogastric curvature, gradual expansion and circular cross sections; shell surface except apical portion lacks ornamentation; apex bluntly pointed, marked by transverse and longitudinal surface lirae; sutures directly transverse; camerae relatively long; siphuncle nearly central in position; septal necks short and orthochoanitic to suborthochoanitic; connecting rings cylindrical; parietal endosiphuncular and mural cameral deposits recognized.

Etymology.—The generic name is derived from the Arbuckle Mountains, and the locality of the type species of the new genus is situated at the northern edge of these mountains.

Discussion.—Possession of the cylindrical connecting rings and the parietal endosiphuncular deposits warrant a subfamilial assignment of Arbuckleoceras gen. nov. In known genera of Spyroceratinae, Arbuckleoceras is most similar to the early Permian genus, Shikhanoceras Shimansky, 1954, from the southern Urals. However, a conspicuous inflation at the embryonic shell, which represents the most characteristic diagnostic feature of Shikhanoceras, is not developed in Arbuckleoceras. Differences in the shapes of the adoral conch, i.e., Arbuckleoceras shows a weak exogastric curvature with circular cross section, whereas Shikhanoceras has orthoconic and laterally compressed conchs. These features are useful to distinguish between these genera.

Dolorthoceras Miller, 1931, is a well known and widespread genus ranging from the Early Devonian to early Permian (Flower, 1939; Sweet, 1964). This genus also resembles Arbuckleoceras, but it differs in having an orthoconic conch and subcylindrical to barrel-shaped connecting rings with an abrupt constriction at the septal foramina. In addition, the camerae of Dolorthoceras are shorter than those of Arbuckleoceras.

Orthoceras tricamerae Smith, 1938, p. 9, pl. 1, figs. 8, 9.

“Orthoceras” sp. A, Ristedt, 1971, pl. 28, fig. 19, pl. 29, fig. 1, pl. 31, fig. 2, pl. 34, fig. 6, pl. 36, figs. 1, 3, 4, pl. 37, figs. 1, 4, 5, pl. 38, figs. 1, 2, 6, 7, 9, pl. 39, figs. 1, 2, 4–6, 9, pl. 42, figs. 2, 6; Tanabe and Uchiyama, 1997, fig. 9.

Orthoceras sp., Blind, 1987, pl. 1, figs. 5, 6, pl. 3, fig. 2, pl. 4, figs. 1–4; text-figs. 2, 5, 7; 1988, text-figs. 1, 5, 7D, 9B, 10A–F; 1991, pl. 1, figs. 1–6, pl. 2, figs. 1–5, pl. 3, figs. 1–6, pl. 4, figs. 1–6, pl. 5, figs. 1–6, pl. 6, figs. 1–6.

Orthoconic nautiloid, Sadd, 1991, figs. 8-A, B; Seuss et al., 2012a, fig. 3C.

Pseudorthoceras sp., Seuss et al., 2009, fig. 17I.

Description.—Longiconic conchs with weak exogastric curvature and circular cross sections; conch expansion is gradual, 4–5° in angle; except for apical portion, shell surface lacks ornamentation; no peristome preserved. Embryonic shell indicates asymmetrical profile in lateral view; apex shifts to ventral side and is bluntly pointed; apical angle approximately 40° in lateral view; the most apical portion of 1.3 mm length from apex has transverse lirae; in addition, weak longitudinal lirae forming cancellate ornamentation are developed on ventral surface of this portion. Sutures directly transverse; camerae relatively long for the family, indicating form ratios (maximum width/length) of 1.5–1.9; siphuncle nearly central in position; siphuncular wall consists of orthochoanitic to suborthochoanitic septal necks and thin connecting rings; length of septal necks short, 0.27–0.29 mm at approximate conch diameter of 4 mm; shapes of connecting rings are cylindrical with very weak constrictions at septal foramina. Endosiphuncular deposits are weak; thin parietal deposits developed on ventral siphuncular wall; cameral deposits mural.

Material examined.—AMNH 5894-5913.

Discussion.—Morphologies of the examined specimens herein agree well with the specific definition of Orthoceras tricamerae Smith, 1938, described from the Buckhorn Asphalt Quarry. The diagnosis of Orthoceras Bruguière, 1789, was emended by Flower (1962) as a genus having three longitudinal furrows at mid-length of the body chamber and the empty siphuncle. Thus, the generic placement by Smith (1938) is revised.

Well preserved embryonic shells of Arbuckleoceras tricamerae were documented by Ristedt (1971) and Tanabe and Uchiyama (1997) as “Orthoceras” sp. A and by Blind (1987, 1988, 1991) as Orthoceras sp. Their results reveal the presence of a distinct cicatrix that is not observed in the present material owing to sediment coverage.

Type species.—Orthoceras bitauniense Haniel, 1915.

Discussion.—See Niko and Nishida (1987) for discussions, including diagnostic emendations, superfamilial to subfamilial assignments and constituent species, of the genus Bitaunioceras.

Orthoceras indianum var. buckhornense Smith, 1938, p. 9, pl. 1, fig. 7.

“Orthoceras” with imbricate ornamentation, Fisher and Teichert, 1969, p. 11, text-fig. 6.

Dolorthoceras incisum Gordon, 1964. Crick, 1982, pl. 1, figs. 1, 4.

Dolorthoceras caneyanum (Girty, 1909). Crick, 1982, pl. 1, fig. 5.

Description.—Longiconic orthocones with circular cross sections and gradual conch expansion, 3–4° in angle; shell surface is ornamented by distant transverse lirae; there are 2—6 lirae per 1 mm at approximate conch diameter of 4 mm; internal mold of conch marked by shallow transverse constrictions due to internal thickening of shell walls; distance of adjoining constrictions nearly equals corresponding conch diameter; peristome and embryonic shell are unknown. Sutures directly transverse; camerae long with maximum width/length ratios of 1.3–1.5; septal curvature deep; siphuncle central in position; siphuncular wall consists of suborthochoanitic septal necks and thin connecting rings; length of septal necks is short, 0.21–0.29 mm at conch diameter of approximately 4 mm; shapes of connecting rings are subcylindrical with weak constrictions at septal foramina. Thick parietal endosiphuncular deposits developed on ventral and dorsal siphuncular walls; ventral deposits form continuous lining; cameral deposits well developed, episeptal-mural and hyposeptal.

Material examined.—AMNH 5977-5991.

Discussion.—The present cephalopod taxon was proposed by Smith (1938) as a variety of Orthoceras indianum Girty (1909, p. 47, pl. 6, figs. 13, 13a) from the Chesterian (Upper Mississippian; = lower Carboniferous) Caney Shale in Oklahoma on the basis of similarities of gross conch shape and surface ornamentation. However, a phylogenetic relationship between these two taxa is uncertain because of the unknown internal morphologies of the Mississippian species.

The transverse constrictions made by internal shell wall thickenings of this species warrant a placement in Bitaunioceras. The discovery from the Desmoinesian rocks represents the oldest and first Pennsylvanian record of this genus. Previous stratigraphic records of the genus range from the Sakmarian (lower Permian) of the southern Urals (Shimansky, 1954) and central Japan (Niko and Nishida, 1987) to the Guadalupian (middle Permian) of Sicily (Gemmellaro, 1890) and northern Mexico (Miller, 1944).

Type species.—Cyrtoceras tuberculatum M'Coy, 1844.

? Thoracoceras sp., Seuss et al., 2009, fig. 17K.

Description.—A single slightly deformed, fragmentary phragmocone, 8.5 mm in length and approximately 1.8 mm in diameter near its adoral end; conch longiconic producing slight curvature, cross section circular and expansion gradual; shell wall longitudinally fluted with ridges and concave interspaces; crests of ridges may be granular; concave septa shallow; camerae relatively short.

Material examined.—AMNH 6113.

Discussion.—Siphuncular structure of the specimen has not been preserved, but it is tentatively placed in Cyrtothoracoceras because its external characters resemble those of C. dombarense Shimansky, 1968, from the lower Carboniferous in the southern Urals.

Type species.—Dolorthoceras circulare Miller, 1931.

Dolorthoceras n. sp., Smith, 1938, p. 6, pl. 1, figs. 13, 14.

? Pseudorthoceras sp., Fisher and Teichert, 1969, p. 11 (part), pl. 1, fig. 2.

Mooreoceras normale Miller, Dunbar and Condra, 1933. Crick, 1982, pl. 1, fig. 8.

Orthoconic nautiloid, Seuss et al., 2012a, fig. 3H.

Diagnosis.—Species of Dolorthoceras with dorsoventrally depressed cross section in apical shell; sutures oblique; cameral length moderate to short with maximum width/length ratios of 2.4–3.6; septal necks short, suborthochoanitic on ventral and cyrtochoanitic on dorsal side; cameral deposits episeptal-mural.

Description.—Couchs longiconic orthocones with gradual to moderate expansion, whose angle is 5–6° in lateral view of post-embryonic shells; cross sections of conchs are dorsoventrally depressed in apical shells, then become circular; shell surface lacks ornamentation; holotype is imperfect phragmocone, 31.5 mm in length and 6.9 mm in dorsoventral diameter near apical end; largest specimen (paratype, AMNH 5953) is imperfect phragmocone approximately 9 mm in diameter; no peristome preserved. Embryonic shells have asymmetrical profile in lateral view, with rounded apex that faintly shifts to ventral(?) side; nepionic constriction occurs at distance of 8.4 mm (paratype, AMNH 5927) and 9.2 mm (paratype, AMNH 5920) from apex; except for apical portion that expands approximately 20° in angle, embryonic shells are nearly cylindrical. Sutures oblique, inclining dorsally with approximate angle of 6–8° for vertical plane to conch axis; septal curvature is moderate with narrow furrow on mid-dorsal region; camerae moderate to short in length; maximum width/length ratios of camera are 2.4–3.6; siphuncle central in position, then shifts ventrally and becomes subcentral in more adoral positions in the conch; siphuncular position ratios (distance of central axis of septal foramen from ventral shell surface per corresponding dorsoventral conch diameter) are 0.48–0.50; siphuncular wall consists of asymmetrical septal necks and thin connecting rings; shapes of septal necks are suborthochoanitic on ventral and cyrtochoanitic on dorsal side; length of septal necks is short, ranging from 0.15 to 0.23 mm in holotype; connecting rings subcylindrical with abrupt constrictions at septal foramina. Endosiphun cular deposits form continuous lining on ventral siphuncular wall; cameral deposits are ventrally thicker than dorsally, episeptal-mural.

Material examined.—Holotype, AMNH 5918. Paratypes, AMNH 5915-5917, 5919-5922, 59245-5927, 5953. In addition, 27 specimens, AMNH 5914, 5923, 5928-5952, are assigned to Dolorthoceras boggyense sp. nov.

Etymology.—The specific name is derived from the type stratum, called the Boggy Formation.

Discussion.—A comparable species, Dolorthoceras medium Gordon (1957, p. 23, pl. 2, figs. 14, 21) from the Upper Mississippian Alapah Limestone of Alaska, with D. boggyense sp. nov. differs in having nearly straight sutures and well developed hyposeptal deposits. A single examined specimen of Dolorthoceras n. sp. in Smith (1938) of 21 mm diameter probably represents the more adoral portion of the new species than the specimens examined here.

Type species.—Orthoceras unicamera Smith, 1938, by monotypy.

Diagnosis.—Conch longiconic orthocone with circular cross sections and very gradual expansion; shell surface ornamented by transverse lirae; deeply curved septa form directly transverse sutures and long camerae; siphuncle central; septal necks orthochoanitic and very long, whose apical tips are weakly bent outwards; connecting rings cylindrical; parietal endosiphuncular deposits partly form continuous lining; cameral deposits episeptal and mural.

Etymology.—The generic name is a combination of the late H. J. Smith, who described cephalopods from the Buckhorn Asphalt Quarry for the first time, and Orthoceras indicating this is an orthoconic cephalopod.

Discussion.—Cameral and siphuncular characters of Smithorthoceras gen. nov. are unique for pseudorthoceratids, and for that reason, they suggest relationships with some orthoceratid genera, including Michelinoceras Foerste, 1932, Mericoceras Zhuravleva, 1978, and Trematoceras Eichwald, 1851. However, the presence of endosiphuncular deposits is an exclusive morphological feature restricted to the Pseudorthoceratidae. We think that similarities between Smithorthoceras and the abovementioned three orthoceratid genera are the results of convergent evolution in the two separate lineages.

The cylindrical connecting rings of Smithorthoceras warrant its placement in the Spyroceratinae. Within the subfamily, Smithorthoceras has a surficial ornamentation similar to that seen in Mitorthoceras Gordon, 1960. However, the latter Late Mississippian genus differs in having a supracentral siphuncular position with suborthochoanitic septal necks (Niko and Mapes, 2015).

Orthoceras unicamera Smith, 1938, p. 7, pl. 1, figs. 1–3.

Michelinoceras directum Unklesbay, 1962, p. 19, pl. 1, figs. 1–3.

“Orthoceras” unicamera Smith. Fisher and Teichert, 1969, p. 11, pl. 1, fig. 1, pl. 2, figs. 2, 3, pl. 3, fig. 3, text-figs. 3A—D, 4A, B, 5A—J; Ristedt, 1971, pl. 31, figs. 1, 3, 5, 6, pl. 32, figs. 2, 4–6, pl. 33, figs. 2, 4–9. pl. 34, fig. 1, pl. 35, figs. 2, 4, 6, pl. 36, figs. 2, 5–8, pl. 38, figs. 4, 5, 8, pl. 39, figs. 7, 8, pl. 40, figs. 1, 3, 5, 6, pl. 41, figs. 4–7, pl. 42, fig. 3, text-fig. 6.

Mitorthoceras crebriliratum (Girty, 1909). Crick, 1982, pl. 1, figs. 3, 6, 7, 11, 12.

Mitorthoceras girty [sic] Gordon, 1964. Crick, 1982, pl. 1, fig. 9.

Mitorthoceras perfilosum Gordon, 1964. Crick, 1982, pl. 1, figs. 10, 13. Michelinoceras? unicamera (Smith). Sturgeon et al., 1997, p. 18, pl. 1–1, figs. 1–7.

Orthoconic nautiloid, Seuss et al., 2012a, figs. 3A, B, D—G.

Description.—Longiconic orthocones with circular cross sections and very gradual conch expansion, approximately 2° in angle; shell surface ornamented by transverse lirae that faintly incline toward venter; there are 9–15 lirae per 1 mm and at conch diameter of approximately 4 mm; peristome and embryonic shell are unknown. Sutures directly transverse; camerae long with maximum width/length ratios of 1.1–1.2; septal curvature deep; siphuncle central in position; siphuncular wall consists of orthochoanitic septal necks and thin connecting rings; apical tips of septal necks weakly bent outwardly; septal necks are very long, 0.85–0.93 mm at conch diameter of approximately 5 mm; ventral septal neck thicker than dorsal one; shapes of connecting rings are cylindrical. Endosiphuncular deposits parietal, forming discontinuous lining on ventral siphuncular wall; cameral deposits differentiated into episeptal and mural.

Material examined.—AMNH 5954-5976.

Discussion.—In addition to the type locality Buckhorn Asphalt Lagerstätte, this species is also recorded from the Desmoinesian of eastern Ohio (Sturgeon et al., 1997).

Type species.—Sueroceras irregulare Riccardi and Sabattini, 1975.

Discussion.—Although the subfamilial assignment of Sueroceras was not determined by Riccardi and Sabattini (1975), its suborthochoanitic septal necks and subcylindrical to fusiform connecting rings indicate that the genus is undoubtedly placed in the Spyroceratinae.

Dolorthoceras oklahomense Smith, 1938, p. 6, pl. 1, figs. 15, 16; Gordon, 1964, p. 119, 120.; Sabattini et al., 2006, p. 1144.

Cancellate “Orthoceras”, Fisher and Teichert, 1969, p. 12, pl. 1, fig. 3, pl. 2, fig. 1.

Kionoceras? sp., Ristedt, 1971, pl. 28, fig. 5, pl. 30, figs. 1–5, pl. 31, figs. 4, 7.

Dolorthoceras oklahomense?. Crick, 1982, pl. 1, fig. 2.

Kionoceras sp., Blind, 1987, pl. 1, fig. 4, pl. 3, fig. 3, text-figs. 2, 6, 7; 1988, text-figs. 1, 5, 7E, 9C; Tanabe and Uchiyama, 1997, fig. 10A—E.

Description.—Examined specimens of small fragmentary phragmocones are longicones with circular cross sections; conch expansion is gradual, approximately 5° in angle; shell surface marked by fine cancellate ornamentation; peristome and embryonic shell are unknown. Sutures directly transverse; cameral length moderate for the family, maximum width/length ratios of 2.0–2.3; siphuncle nearly central in position; siphuncular wall consists of orthochoanitic septal necks and thin connecting rings; length of septal necks short, 0.21–0.22 mm at approximate conch diameter of 3 mm; shapes of connecting rings are cylindrical with weak constrictions at septal foramina. Endosiphuncular deposits are weak; thin parietal deposits developed on ventral siphuncular wall; cameral deposits mural.

Material examined.—AMNH 5992–5996.

Discussion.—Judging from their morphologies described above, the newly collected specimens are conspecific with Dolorthoceras oklahomense described from the same locality by Smith (1938). Herein, we classify D. oklahomense within Sueroceras because of possession of the cancellate surface ornamentation. Sabattini et al. (2006) previously suggested the possibility of the same reassignment.

Type species.—Sulphurnites taffi sp. nov., by monotypy.

Diagnosis.—Conch longiconic orthocone with circular cross sections and gradual expansion; shell surface lacks ornamentation; septa deeply concave; camera relatively long to moderate in length; sutures directly transverse; siphuncle nearly central; septal necks short and suborthochoanitic; connecting rings subcylindrical to fusiform; endosiphuncular deposits initiate at apical and adoral junctions between septal neck and connection ring, then they mainly grow posteriorly and anteriorly; cameral deposits episeptal-mural and hyposeptal.

Etymology.—The generic name is derived from the rural community of Sulphur, Murray County, Southcentral Oklahoma. The type locality is situated approximately 10 km south of the outskirts of this community.

Discussion.—Endosiphuncular deposits of Sulphurnites gen. nov. are unique for the family Pseudorthoceratidae (see also Seuss et al., 2012a, figs. 7A1, 7A2, 7B, 7C2–6), whose incipient deposits mostly occur on septal necks. Similar deposits are also known from the Ordovician genus, Mysterioceras Teichert and Glenister, 1953, whose incipient deposits originate immediately behind septal necks. Except for the endosiphuncular deposits, the characters of Sulphurnites clearly correspond to those of the Spyroceratinae.

Orthoconic nautiloid, Seuss et al., 2012a, figs. 2, 4A—F, 5A—F, 6A—F, 7A1, 7A2. 7B, 7C1—6.

Orthoconic nautiloid (Pseudorthoceratidae gen. et sp. indet.), Seuss et al., 2012b. figs. 3, 4A, B, 6A—C, 7A—H 8B—D.

Diagnosis.—As for the genus.

Description.—Both available specimens are imperfect phragmocones, which are longiconic orthocones with circular cross sections and unornamented shell surface; expansion angle of conch is gradual, approximately 4°; the holotype is 43.5 mm in length and 8.1 mm in diameter near its adoral end; a paratype attains approximately 22 mm in diameter; no peristome and no embryonic shell preserved. Sutures directly transverse; cameral length relatively long to moderate for the family with maximum width/length ratios of 1.7–2.0; septa deeply concave; siphuncle nearly central in position; siphuncular wall consists of suborthochoanitic septal necks and thin connecting rings; outward curvature of septal necks is faint; length of septal necks is short, ranging from 0.52 to 0.61 mm in the holotype; connecting rings exhibit weak inflations in camerae and distinct constrictions at septal foramina, forming subcylindrical to fusiform profiles. Incipient parts of endosiphuncular deposits occur at apical and adoral junctions between septal neck and connecting ring on ventral siphuncular wall; among them, apical deposits mainly extend posteriorly and adoral ones mainly extend anteriorly; surface of septal necks and dorsal siphuncular wall are not covered by endosiphuncular deposits; cameral deposits well developed, differentiated into episeptalmural and hyposeptal.

Material examined.—Holotype, AMNH 5997. Paratype, BSPG 2011 0002.

Etymology.—This species is named in honor of the late J. A. Taff in recognition of his contributions to the geology in Oklahoma.

Discussion.—Weak conch curvature is obscure in the examined fragmentary specimens. Thus, in such material Sulphurnites taffi sp. nov. shares similar external characters with an associated species, Arbuckleoceras tricamerae (Smith, 1938; see above). However, the latter species can be distinguished by the presence of cylindrical connecting rings and the absence of hyposeptal deposits.

Type species.—Unklesbayoceras striatulum sp. nov. by monotypy.

Diagnosis.—Couchs longiconic with weak endogastric curvature, moderate expansion and circular cross sections; shell surface ornamented by transverse lirae; sutures directly transverse; camerae long to relatively long; siphuncle nearly central and supracentral in position; septal necks long and suborthochoanitic; connecting rings cylindrical with constrictions at septal foramina; endosiphuncular deposits form thick lining on ventral siphuncular wall; cameral deposits episeptal-mural.

Etymology.—The generic name is to honor the late A. G. Unklesbay, in recognition of his contributions to the study of upper Paleozoic cephalopods in North America.

Discussion.—Unklesbayoceras gen. nov. has several synapomorphies found with the Spyroceratinae, such as suborthochoanitic septal necks and cylindrical connecting rings. Of the genera included in this subfamily, Unklesbayoceras exhibits similarities with the Mississippian genus Mitorthoceras Gordon, 1960 (see Niko and Mapes, 2015 for the emended diagnosis of the genus). However, the new genus differs from Mitorthoceras in having weak endogastric curvature of the conch, longer camerae and a less eccentric siphuncular position.

Diagnosis.—As for the genus.

Description.—Longiconic conch with weak endogastric curvature and circular cross section; conch expansion of approximately 6° is moderate for the family; the holotype only known specimen of an imperfect phragmocone is 26.0 mm in length and 6.1 mm in apical diameter; shell surface ornamented by weak transverse lirae that faintly incline toward venter; there are 9–15 lirae at a conch length of 1 mm; body chamber and embryonic shell not preserved. Sutures directly transverse, except for narrow dorsal furrow; septal concave curvature is relatively deep; camerae long to relatively long for the family, indicating form ratios (maximum width/length) of 1.1–1.5; siphuncle near central axis of conch and faintly supracentral; siphuncular position ratio (distance of central axis of septal foramen from ventral shell surface per corresponding conch diameter) is 0.53; siphuncular wall consists of suborthochoanitic septal necks and thin connecting rings; length of septal necks is long, 0.52–0.75 mm; shapes of connecting rings are cylindrical with constrictions at septal foramina. Endosiphuncular deposits well developed, to form thick lining on ventral siphuncular wall; thin parietal deposits developed on ventral siphuncular wall; cameral deposits episeptal-mural.

Etymology.—The specific name is derived from the Latin, striatulus (= having weak lirae), referring to the surface ornamentation.

Material examined.—Holotype, AMNH 6114.

Discussion.—This species is represented by a single, well preserved specimen. Its distinctive features including endogastric conch curvature, cameral nature and siphuncular position are sufficiently pronounced to warrant establishing a new genus and species.