Type Species: Inoceramus cuvieri Sowerby, 1814, by subsequent designation of Cox, 1969: 315.

Material: Two single left valves; TMP 2016.041.0097 from Wapiabi Creek and TMP 2016.041.0233 from West Thistle Creek.

Measurements: See table 1.

Description: TMP 2016.041.0097 (fig. 5A, B) is a moderately large (hmax = 84.5 mm) left valve (LV) internal mold, with the disc well preserved, but with the posterior auricle missing. The disc is triangular in outline, orthocline, with the beak curved anterodorsally, projecting slightly above the hinge line. The anterior margin is long, concave below the umbo, straight ventralward. The ventral margin is regularly rounded. The disc is weakly to moderately inflated, with maximum inflation in the umbonal part. The anterior wall is moderately high, steep, and almost perpendicular to the commissure below the umbo. The disc is ornamented with widely spaced, apparently regular (although deformed in our specimen) commarginal rugae, slightly asymmetrical with their leading edges slightly steeper, and with rounded edges and interrugae spaces.

TMP 2016.041.0233 (fig. 5E, F) is an internal mold of the moderately large LV (hmax = 100.5 mm), with its beak and most of its posterior auricle missing. The preserved fragment of the posterior auricle suggests, however, that it was extended and relatively large, of the type similar to Inoceramus lusatiae Andert. This specimen differs from TMP 2016.041.0097 in possessing a less steep anterior wall below the umbo and in the presence of a better-developed radial sulcus, posteriorly of the disc axis. The sulcus is shallow and poorly developed; it begins at approximately 35 mm axial distance. The ornament is of the same type in both specimens.

Discussion: The two specimens clearly belong to the Inoceramus lamarcki group. They may be closely allied to Inoceramus annulatus Goldfuss, 1836, or Inoceramus lusatiae Andert, 1911 (the latter is suggested by the type of the posterior auricle in the larger specimen). From both of these species, our specimens differ in possessing the radial sulcus. This feature appears in various lineages/ clades of the “lamarcki” group (e.g., in the Turonian Inoceramus hobetsensis Nagao and Matsumoto, 1939, Inoceramus flaccidus White, 1879, or in Turonian representatives of Inoceramus lamarcki Parkinson, 1819, as known from the U.S. Western Interior; see Noda, 1975, Kauffman, 1977; Kauffman et al., 1978, Noda and Matsumoto, 1998, Walaszczyk and Cobban, 2000), but its taxonomic significance is not clear (Noda, 1975; Noda and Matsumoto, 1998).

Occurrence: Both specimens are from the topmost part of the lower Coniacian.

1877. Inoceramus gibbosus Schlüter: 271.

1888. Inoceramus percostatus Müller: 413, pl. 17, fig. 3.

?non 1911. Inoceramus percostatus Müller. Andert: 56, pl. 5, fig. 4.

1929. Inoceramus dankeri Heinz var. anderti Heinz. Heinz: 686, figs. 4–5.

1929. Inoceramus gibbosus Schlüter. Heine: 50, pl. 4, figs. 20–22.

1929. Inoceramus percostatus Müller. Heine: 46, pl. 3, figs. 14–17.

1929. Inoceramus bilobatus Müller. Heine: 49, pl. 4, figs. 18–19.

?non 1934. Inoceramus percostatus Müller. Andert: 119, pl. 5, fig. 4.

1958. Inoceramus russiensis Nikitin. Bodylevski: 78, pl. 29, fig. 1; pl. 31, fig. 1.

1959. Inoceramus percostatus Müller. Drobrov and Pavlova: 145, pl. 12, fig. 3.

non 1963. Inoceramus percostatus Müller. Assmus: 45, pl. 9, fig. 1.

?non 1969. Inoceramus percostatus Müller. Khalafova: 177, pl. 13, fig. 4; pl. 14, fig. 1 [pl. 13, fig. 4 = deformis group; pl. 14, fig. 1 = ?Tethyoceramus sp.]

1972. Inoceramus percostatus Müller. Glazunova: 59, pl. 2, figs. 1–2; pl. 3, fig. 2; pl. 9, fig. 1, pl. 13, fig. 6.

1972. Inoceramus percostatus Müller subsp. gorenkaensis subsp. nov., Glazunova: 60, pl. 4, figs. 1–2; pl. 6, figs. 1–2; pl. 7, fig. 1; pl. 9, fig. 2.

2006. Inoceramus gibbosus Schlüter, 1877. Walaszczyk and Cobban: 273; text-figs. 21, 12.11 and 13.5.

Type: The holotype, by monotypy, is the original of Schlüter (1877: 271) first illustrated by Heine (1929: pl. 4, figs. 20–22) from the upper Coniacian of Osterfeld Mine near Oberhausen, in Westphalia, northern Germany.

Material: Twenty-six specimens in total, most of which are fragmentarily preserved. TMP 2016.041.0110 through 2016.041.0127, from Blackstone River. TMP 2016.041.0236 from Thistle Creek. TMP 2016.041.0098, 2016.041.0089, 2016.041.0090, and 2016.041.0095, from Wapiabi Creek. TMP 2016.041.0170 and 2016.041.0172 from Chungo Creek. One unnumbered specimen from Sheep River.

Measurements: See table 1.

Description and remarks: Most of the specimens in our collection are small-sized, juvenile fragments from the Blackstone River section. They show, however, the upright form, pointed beak, and triangular outline, with well-developed, distinct rugae, covered with well-developed, sharp-edged growth lines, typical for the species.

The best preserved is specimen TMP 2016.041.0110 from Blackstone River; the major part of the adult stage is well preserved (fig. 5D). Its umbonal part is poorly preserved (deformed), as is its anterior part. The disc, within the preserved part, is subrectangular in outline, and possesses a distinct radial sulcus posteriorly of the growth axis. The sulcus is shallow and does not deform the concentric rugae. The concentric rugae are regular to subregular, symmetrical, with rounded edges. They are covered with sharpe-edged growth lines, which are evenly developed on the entire height of the disc.

The juvenile fragment from Sheep River (fig. 5C) possesses a well-preserved posterior auricle, which is extended and well separated from the disc, along a well-developed auricular sulcus. The disc is covered with subregular concentric rugae, superimposed by raised sharp-edged growth lines that are typical of the species.

The medium-sized incomplete specimen TMP 2016.041.0172 (fig. 5G), from Chungo Creek, demonstrates well the general outline of the species and type of ornament. The posterior part of its disc, with the posterior, radial sulcus, is deformed and partly missing.

Occurrence: The species (as herein interpreted) is known from the Wapiabi Formation from localities on Blackstone River, Wapiabi Creek, West Thistle Creek, Sheep River, and Chungo Creek. It occurs invariably in the topmost part of the lower Coniacian, disappearing below the entry of the first Volviceramus. The species, as herein understood, was first precisely located in the stratigraphic succession of the Staffhorst Mine section, in northern Germany (Walaszczyk and Wood in Niebuhr et al., 1999), where it occurs in an equivalent stratigraphic interval. Although the species was also reported from other regions (e.g., eastern part of European Russia; see, e.g., Nikitin, 1888; Glazunova, 1972), precisely located specimens have not been reported.

1888. Inoceramus kleini, sp. nov. G. Müller: 415, pl. 18, fig. 1a–b.

?pars 1911. Inoceramus kleini Müller. Andert: 48–50, pl. 2, fig. 6 [non pl. 1, fig. 7; pl. 2, figs. 3, 7–8].

non 1934. Inoceramus kleini Müller. Andert: 115–117, text-figs. 10–12. pl. 4, figs. 9–10; pl. 5, figs. 1–2.

1929. Inoceramus kleini Müller. Heine: 44–46, pl. 2, figs. 10–11; pl. 3, figs. 12–13.

1969. Inoceramus kleini Müller. Radwanska: 709.

1979. Inoceramus kleini Müller. Ivannikov: 62, pl. 14, fig. 4; pl. 15, figs. 1–2; pl. 16, fig. 1; pl. 17, fig. 1.

pars 1991. Inoceramus kleini Müller. Tarkowski: 109–110, pl. 13, fig. 7; pl. 14, fig. 2 [non pl. 14, fig. 3].

1992. Inoceramus kleini Müller. Walaszczyk: 37; pl. 38, fig. 3.

1992. Inoceramus kleini Müller. Cech and Svabenicka, pl. 2, fig. 2.

Type: By monotypy, the holotype is the specimen figured by Müller (1888, pl. 18, fig. 1a–b) from the Spiegelsberge, south of Halberstadt (Subhercynian Basin), Germany; from the middle Coniacian.

Material: Two specimens in total. Doublevalve TM P 2016.041.0407, from Bighorn Dam, and one uncataloged, juvenile fragment of a single valve from West Thistle Creek.

Measurements: See table 1.

Description: The double-valve specimen, TMP 2016.041.0407 (fig. 6A–C), is weakly deformed, almost complete, with posteroventral parts of valves missing. The specimen is equivalve, inequilateral, small sized, and prosocline, with the disc subtriangular in outline and moderately inflated. The posterior auricle is small, moderately well separated from the disc. The beak is pointed, curved anterodorsally. Anterior margin is slightly concave below the umbo, then slightly convex; with the anterior margin steep. The ornament is composed of regularly spaced, symmetrical rugae, with interspaces growing gradually ventralward. The edges of the rugae are sharp. The rugae weaken on the posterior auricle and on the anterior wall, but are still visible.

Remarks: The species is interpreted herein as the evolutionary precursor of Inoceramus undabundus Meek and Hayden. Early representatives of the latter species are similar in valve outline and type of ornament, however, the interspaces are much larger at equivalent axial length.

Occurrence: The species spans the lower to middle Coniacian boundary. Although we have only two specimens (one from the topmost lower Coniacian in West Thistle Creek; and the second from the basal middle Coniacian at Bighorn Dam), this stratigraphic occurrence corresponds well with its occurrence in other areas. The species is known from Germany, Poland, Russia, Romania, and the Czech Republic.

1862. Inoceramus undabundus Meek and Hayden: 26.

1876. Inoceramus undabundus Meek and Hayden. Meek: 60, pl. 3, fig. 2.

1894. Inoceramus undabundus Meek and Hayden. Stanton: 84, pl. 16, figs. 1–2 [illustration and description after Meek, 1876].

1898. Inoceramus undabundus Meek and Hayden. Logan: 455, pl. 105, figs. 1–2. [illustration and description after Meek, 1876]

?1901. Inoceramus undabundus Meek and Hayden. Sturm: 92, pl. 10, fig. 4.

pars 1929. Inoceramus undabundus Meek and Hayden. Heine: 100, pl. 11, fig. 50; pl. 13, fig. 57 [non pl. 11, fig. 51; pl. 19, fig. 71, which are Volviceramus exogyroides Meek and Hayden]

pars 2006. Inoceramus undabundus Meek and Hayden, 1862. Walaszczyk and Cobban: 260; text-figs. 9.2, 9.4, 27.2, 28.2, 38.6 [only]

Type: The lectotype, designated by Walaszczyk and Cobban (2006: 260), is USNM 1909, which is the original of Meek (1876: pl. 3, fig. 2), from the Marias River Shale of Chippewa Point near Fort Benton, Choutea County, Montana.

Material: Seven specimens; TMP 2016.041.0402, TMP 2016.041.0403, TMP 2016.041.0426, TMP 2016.041.0427, TMP 2016.041.0434; all from the Bighorn Dam section; TMP 2016.041.0244 from West Thistle Creek; and TMP 2016.041.0196 from Chungo Creek.

Measurements: See table 1.

Description: The typical specimens of the species are TMP 2016.041.0426 (fig. 7A, D), TMP 2016.041.0427, TMP 2016.041.0434, and TMP 2016.041.0244. Based on these four specimens, the characteristic of the species is as follows. The shell is inequivalve, with LV larger and more inflated than the right valve (RV), with a general architecture typical for Volviceramus. Both valves grow obliquely, with δ angle ranging between 30° and 45°. The beaks in both valves pointed, only slightly coiled, not projecting above the hinge line. The oblique growth continues till ca. 10 cm in axial length, the obliquity is then markedly reduced. Both valves are ornamented with strong commarginal rugae, with distinct ventralward increase of interspaces. The details of the shell are not known; the rugae on internal molds are symmetrical to moderately asymmetrical, with leading edges steeper. The interspaces are distinctly wider than the rugae edges. The edges of the rugae are rounded.

The smallest specimen, which comes from the basal middle Coniacian and apparently phylogenetically the oldest (2016.041.0402; fig. 7B, C), is only slightly inequivalve. It already possesses, however, the typical ornament. TMP 2016.041.0403 from Bighorn Dam and TMP 2016.041.0196 from Chungo Creek, are fragments of LVs.

Discussion: The material studied includes the first well-documented RVs of the species ever reported.

Although in our material the species is represented by only seven specimens, they demonstrate the evolution of the species from a relatively small-sized, weakly inequivalve morphotype (fig. 7B, C), in the earliest middle Coniacian, to moderate size, markedly inequivalve more advanced morphotype stratigraphically higher (fig. 7A, D). The phylogenetically oldest, weakly inequivalve specimens closely resemble Inoceramus kleini, from which they differ in having more robust ornament. The phylogenetically more advanced specimens possess features typical for volviceramids; this is particularly well seen on the RVs, in which the beak moves ontogenetically from its marginal position gradually inward (fig. 7A), as a consequence of inequivalve growth of the valve. Based on its evolutionary interpretation, the species (as a successor of Inoceramus kleini) is left in the genus Inoceramus, in spite of its close morphological resemblance to Volviceramus.

Walaszczyk and Cobban (2006) included into the synonymy of Inoceramus undabundus also Inoceramus stantoni (= I. acuteplicatus of Stanton, 1894) Sokolov, 1914. Based on the Canadian material, however, it seems that phylogenetic changes of both species differ. In contrast to I. undabundus, I. stantoni remained only slightly inequivalve and preserved its more subtle ornament. Consequently we keep both species separate here. Both I. undabundus and I. stantoni seem to originate from I. kleini.

Occurrence: Inoceramus undabundus is most abundant in the Bighorn Dam section, where it was found at levels 41.0, 60.0, and 73.0 m. The single specimen from West Thistle Creek is from 72.4 m, and the specimen from Chungo Creek is from 54.0 m. The species is known from the U.S. Western Interior and Gulf Coast of North America. It is convincingly documented from Poland (Sturm, 1901) and Germany (Heine, 1929).

Type Species: Inoceramus (Tethyoceramus) basseae Sornay (1980: pl. 1, figs. 1, 4, 6; pl. 2, figs. 1–3) by original designation.

Diagnosis and Discussion on the Genus: See Walaszczyk and Wood (1998).

Material: Six specimens in total. Single unnumbered specimen from Mill Creek, from 76.6 m; 4 specimens from Bighorn Dam: TMP 2016.041.0395 and TMP 2016.041.0391 from 8.5 m; TMP 2016.041.0398 from 10.5 m; and TMP 2016.041.0400 from 41.5 m. Single specimen from Highwood River, TMP 2016.041.0139.

Remarks: The genus is relatively rare in the studied material, similar to the equivalent succession of the U.S. Western Interior (Walaszczyk and Cobban, 2000). Most of the specimens are poorly preserved, incomplete single valves. Two left valves of specimen TMP 2016.041.0395 (fig. 8) resemble Tethyoceramus alpinus (Heinz) (the smaller specimen) and Tethyoceramus ernsti (Heinz) (the larger one). To the latter species may also be referred the huge specimen from Highwood River (TMP 2016.041.0139). TMP 2016.041.0400 (not illustrated) is referred herein to Tethyoceramus wandereri (Andert), based on its very slender form and strong inflation.

Occurrence: The genus is known from the mid lower Coniacian in Europe and in the American Western Interior (see Walaszczyk and Wood, 1998; Walaszczyk and Cobban, 2000), and is well represented in Madagascar, where it apparently starts at the topmost Turonian and ranges through most of the lower Coniacian (Sornay, 1980; Walaszczyk et al., 2004, 2014a).

Type Species: By original designation, Inoceramus inconstans Woods, 1912, from the lower Coniacian (Cox, 1969: N315).

Material: Forty-one specimens in total. Seven specimens from Chungo Creek: TMP 2016.041.0176 though to TMP 2016.041.0180 from 33.5 m; TMP 2016.041.0175 from 34.5 m; and TMP 2016.041.0174 from 37 m. Two specimens from West Thistle Creek; TMP 2016.041.0239 and TMP 2016.041.0237, both from 28.5 m. Nine specimens from Blackstone River: TMP 2016.041.0102 from 6.5 m; TMP 2016.041.0103 from 13.6 m; TMP 2016.041.0132 from 20.5 m; TMP 2016.041.0133 from 38.2 m; TMP 2016.041.0134 from 39.4 m; and TMP 2016.041.0128 through to TMP 2016.041.0131, from 43.5 m. Four specimens from Wapiabi Creek: TMP 2016.041.0096 from 2.8 m; TMP 2016.041.0101 from 7.9 m; TMP 2016.041.0100 from 48.5 m; and TMP 2016.041.0089 from 54.7 m. Six specimens from Sullivan Creek: TMP 2016.041.0078 through to TMP 2016.041.0083, from the inconstans interval. Single, unnumbered specimen from Cutpick Creek. Eight specimens from Bighorn Dam: TMP 2016.041.0389 through to TMP 2016.041.0394 from 8.5 m; TMP 2016.041.0397 from 10.5 m; TMP 2016.041.0401 from 32.5 m; and TMP 2016.041.0396 from 34.0 m. Four specimens from Highwood River: TMP 2016.041.0141, TMP 2016.041.0142, TMP 2016.041.0143, and TMP 2016.041.0146.

Remarks: The taxonomy and evolutionary interpretation of the genus, as applied herein, follows Walaszczyk and Wood (1998) and Walaszczyk and Cobban (2000), with slight modification, as discussed below.

The genus is well represented in the lowermost part of the Wapiabi Formation, up to surface CS4. The cremnoceramid assemblage is composed of Cremnoceramus deformis deformis (Meek, 1871), Cremnoceramus crassus crassus (Petrascheck, 1903), and Cremnoceramus crassus inconstans (Woods, 1912). This is the same assemblage as known from the southern part of the Western Interior Basin (see Walaszczyk and Cobban, 2000), and outside, in other areas of the Euramerican biogeographic region (e.g., Walaszczyk, 1992; Walaszczyk and Wood, 1998). The form that dominates the assemblage is C. deformis deformis (fig. 9A, D); less common is C. crassus crassus (fig. 9B). What is very interesting is the parallel occurrence of C. crassus crassus and typical forms of C. crassus inconstans (fig. 10). This may suggest that the change from C. crassus inconstans to C. crassus crassus was cladogenetic in character and both forms co-occurred subsequently. Consequently, both should be simply referred to as C. crassus and C. inconstans.

Occurrence: The genus is well represented in all localities studied herein spanning the lower Coniacian: Cutpick Creek, West Thistle Creek, Bighorn Dam, Chungo Creek, Ram River, Sheep River, Wapiabi Creek, Blackstone River, and Highwood River (fig. 1). The genus is known from the Euramerican biogeographic region (western Central Asia, Europe, and the Atlantic and gulf coasts of North America; North American Western Interior) (Tröger, 1981, 1989; Walaszczyk, 1992; Kauffman et al., 1993; Walaszczyk et al., 1998; Walaszczyk and Cobban, 1998, 2000; Wood et al., 2004); North Pacific Province (Japan, Sakhalin) (Noda, 1996), New Zealand (Crampton, 1996), South America (Brazil) (Kauffman and Bengtson, 1985).

Type Species: Inoceramus involutus J. de C. Sowerby: 1828: 160, pl. 583, figs. 1–3, by original designation (Stoliczka, 1871: 394, 401).

Remarks: Woods (1912) regarded Volviceramus as a successor of the Inoceramus lamarcki Parkinson group. However, as rightly pointed out by Tsagarély (1942), both the valve outline (particularly the RV) and the ornament of Volviceramus are close to Cremnoceramus (Inoceramus inconstans in Tsagarély, 1942). The single RV of various species, as well as the juveniles LV of V. cardinalensis, sp. nov., or V. exogyroides can very easily be mistaken for Cremnoceramus. Both Volviceramus and Cremnoceramus also show similar morphological variability in juvenile obliquity of growth. In the case of Volviceramus this is well seen in LVs; this feature is difficult to evaluate in case of RVs.

Through its distinct inequivalvness, the genus is very easily separated from other inoceramids. Some inequivalve representatives of the genus Inoceramus, as, e.g., Inoceramus inaequivalvis Schlüter, 1877, differ from Volviceramus in being distinctly less inequivalve (and they are never coiled) and in possessing more or less similar ornament on both valves.

Volviceramids appear abuptly above CS4, which caps a prominent, sandier-upward heterolithic succession of the lower Coniacian. Already within the lowest middle Coniacian allomembers (CA5–6) the variability of the genus is remarkable. There appear: Volviceramus koeneni (Müller), V. exogyroides (Meek and Hayden), and V. cardinalensis, sp. nov. In addition to a single specimen, which shows a transitional character between V. exogyroides and V. involutus, the latter species was not noticed in this lowest interval; the first typical representatives of V. involutus are from allomember CA8.

The intraspecific variability within Volviceramus is caused mainly by the variability in the juvenile obliquity in their LVs. This allows the distinction of two morphogroups within the clade. The first group comprises low-obliquity forms (with high juvenile δ angle), characterized by a coiled or uncoiled, slender general outline. The group is represented by: V. koeneni, V. involutus, and V. stotti, sp. nov. The second group comprises forms growing obliquely in the juvenile stage (low juvenile δ angle), changing the direction of growth, to a less oblique one, later in ontogeny. This leads to a similar final architecture of the valve as the one observed in strongly inflated cremnoceramids. The oblique juvenile growth causes marked increase in valve length, and combined with subsequent geniculation and change to distinctly lower obliquity, gives a broad morphotype with massive appearance. The group is represented by V. exogyroides and V. cardinalensis, sp. nov. (see figs. 13–17). Whereas, however, the LVs in this second group resemble strongly geniculated valves in Cremnoceramus, their RVs are distinctly smaller, nongeniculated, with the typical Volviceramus RV geometry.

Occurrence: The documented range of Volviceramus is middle to upper Coniacian. The genus is known from the Euramerican biogeographic region (western Central Asia, Europe, Gulf of Mexico area, American Western Interior).

1888. Inoceramus (Volviceramus) Koeneni n.sp., Müller: 412, pl. 17, fig. 1.

1891. Inoceramus paradoxus v. Haenlein. Langenhan and Grundey: 12, pl. 5, figs. 3–4.

1891. Inoceramus varius v. Haenlein. Langenhan and Grundey: 12, pl. 5, figs. 1; ?pl. 5, fig. 2.

1913. Inoceramus (Volviceramus)(aff.?) involutus Sowerby. Scupin: 213, pl. 12, fig. 3.

1928. Inoceramus koeneni Müller. Heinz: 37, pl. 3, fig. 2.

1929. Inoceramus koeneni Müller. Heine: 98, pl. 15, fig. 63; pl. 17, fig. 66; pl. 18, fig. 67.

1932. Rhadinoceramus regalis, sp. nov., Heinz: 21.

non 1933. Cymatoceramus (Cymatoceramus) cf. koeneni Müller. Heinz: 253; pl. 19, fig. 3 [= Tethyoceramus basseae Sornay]

1934. Inoceramus koeneni Müller. Andert: 132, text-figs. 16a–c; pl. 8, figs. 2–3.

?1959. Inoceramus involutus Sowerby. Dobrov and Pavlova: 153; pl. 10, fig. 1.

?1968. Inoceramus koeneni Müller. Kotsubinsky: 135; pl. 23, figs. 4, 5

1969. Inoceramus koeneni G. Müller. Tröger: 68, pl. 1, figs. 1–6; pl. 2, figs. 1–5.

1974. Inoceramus koeneni G. Müller. Tröger, pl. 5, figs. X4302, X4303, X4305, X4306.

1991. Inoceramus (Volviceramus) koeneni Müller. Tröger and Christensen: 31, pl. 3, fig. 7; ?pl. 2, figs. 2–3.

1994. Volviceramus koeneni (G. Müller, 1888). Tröger and Summesberger: 169, pl. 2, figs. 1–3.

non 1994. Inoceramus (Volviceramus) cf. koeneni Müller. Malchus et al.: 116, text-fig. 4a, pl. 1, fig. 7 [=Cordiceramus cordiforis]

?non 1996. Inoceramus (Volviceramus) koeneni Müller, 1888. Noda: 566, fig. 10.

?non 1998. Inoceramus (Volviceramus) koeneni Müller, 1887. Noda and Matsumoto: 459, pl. 13, fig. 3. [reillustrated specimen of Noda, 1996: fig. 10]

2006. Volviceramus koeneni (Müller, 1888). Walaszczyk and Cobban: 282; text-fig. 24, 25.2–25.4, 29.2.

Type: The lectotype, by subsequent designation of Tröger (1969), is the original of Müller (1888: pl. 17, fig. 1) from the middle Coniacian of Lehofsberg, near Quedlinburg, Germany.

Material: Nine specimens in total. Single specimen, TMP 2016.041.0076, from Sullivan Creek. Eight specimens from Chungo Creek: complete, double-valve TMP 2016.041.0184; TMP 2016.041.0182, TMP 2016.041.0183 (2 specimens), and TMP 2016.041.0187, and TMP 2016.041.0189 (2 specimens). Single specimen (cf.) from Sheep River, TMP 2016.041.0333.

Measurements: See table 1.

Description: TMP 2016.041.084 (fig. 11) is a well-preserved double-valved specimen, almost complete (a small fragment of the anterior part of the LV is missing), slightly deformed; with much of its shell intact. LV is107 mm high; RV is 90 mm high. Both valves are slender (with b/h ration 0.56 and 063 in the RV and LV respectively), however, this is partly due to secondary deformation perpendicular to the commissure. The LV is more inflated than the RV; its h/b ratio being 0.54. The LV juvenile growth is slightly oblique, with δ angle c. 75°. At h = 60 mm, δ angle increases to 90°. Its beak is pointed and curved dorsally. The LV bears weak, poorly developed commarginal rugae. In the ventral part it is almost smooth. The RV is moderately inflated; its b/h ratio is 0.42. Its obliquity is almost constant, with δ approximating 90°. The anterior wall is steep, high, and slightly concave. The posterior auricle is well separated from the disc, with a distinct sulcus in the dorsal part. The beak is pointed, projecting above the hinge line. The disc is ornamented with well-developed commarignal rugae, superimposed by radial sulci in the axial part of the midadult stage (fig. 11D).

TMP 2016.041.082, TMP 2016.041.087, and TMP 2016.041.0333 are juvenile fragments of the LVs, undeformed; TMP 2016.041.0333 is with fragments of shell intact. They are referred to the Müller's species based on their ornamented valve.

The double valve specimen TMP 2016.041.0189 is complete, moderately large specimen (hmax of RV = 104 mm), strongly deformed. It is moderately inequivalve, with the LV almost smooth, and with strong, typically ornamented RV.

Remarks: V. koeneni is morphologically the closest to V. involutus. The differences are (see Tröger, 1969) that V. involutus exhibits: stronger inequivalvness, lack of undulation on the LV, and distinctly stronger inflation and coiling of LV. Transitional forms between both species occur. The stronger inflation of the RV in V. koeneni than in V. involutus, mentioned by Müller (1888), is difficult to evaluate; one would need two-valve specimens, which are extremely rare. Volviceramus koeneni is the oldest member of the Volviceramus clade.

Cymatoceramus (Cymatoceramus) cf. koeneni Müller from Madagascar, illustrated by Heinz (p. 253; pl. 19, fig. 3), is Tethyoceramus basseae (Sornay) as shown by Sornay (1980). To Tethyoceramus also belongs, most probably, the specimen of Inoceramus (Volviceramus) koeneni as reported from Japan by Noda (1996: fig. 10; see also Noda and Matsumoto, 1998: pl. 13, fig. 3). The Japanese specimen shows a regular pattern of concentric rugae, typical for Tethyoceramus/Cremnoceramus.

Occurrence: Volviceramus koeneni spans the middle Coniacian. At the base of the middle Coniacian it forms a distinct interval zone, being followed by V. involutus (see also Müller, 1900; Stille, 1909; Heinz, 1928; Tröger, 1969). It is known from the Euramerican biogeographic region; neither the Madagascan report (Heinz, 1933) nor the Japanese one (Noda, 1996) can be confirmed.

1828. Inoceramus involutus J. de C. Sowerby: vol. vi: 160, pl. 583, figs. 1–3

1846. Inoceramus involutus Sowerby. d'Orbigny, vol. iii: 520, pl. 413, figs. 1–3.

1846. Inoceramus lamarcki d'Orbigny, vol. iii: 518, pl. 412.

1850. Inoceramus involutus. Dixon: pl. 28, fig. 32.[= Volviceramus anglo-germanicus of Heinz, 1932; = Inoceramus involutus belovodiensis of Glasunova, 1972]

1858. Inoceramus umbonatus Meek and Hayden: 50.

1871. Inoceramus (Volviceramus) involutus Sowerby. Stoliczka: 394, 401

1876. Inoceramus umbonatus Meek and Hayden. Meek: 44, pl. 3, fig. 1; pl. 4, fig. 1–2.

1888. Inoceramus (Volvicerasmus) involutus Sowerby. Müller: pl. 16, figs. 3, 4,

1901. Inoceramus involutus Sowerby. Sturm: pl. 9, fig. 4.

1902. Inoceramus involutus Sowerby. Wollemann: pl. 1, fig. 4; pl. 2, figs. 7, 8

1907. Inoceramus umbonatus Meek and Hayden. Veatch: pl. 10, fig. 2.

1912. Inoceramus involutus Sowerby. Woods: 327, text-figs. 88–94.

1932. Volviceramus anglo-germanicus Heinz: 22. [=Inoceramus involutus Sowerby; Dixon, 1850, pl. 28, fig. 32]

?1959. Inoceramus involutus Sowerby. Dobrov and Pavlova: 153, pl. 10, fig. 1a, b.

1972. Inoceramus involutus Sowerby subsp. belovodiensis Glazunova, subsp. nov., Glazunova: 63; pl. 8, fig. 1; pl. 12, figs. 1, 2; pl. 13, fig. 5.

1974. Inoceramus involutus Sowerby. Kotsubinsky: 81, pl. 18.

2006. Volviceramus involutus (J. de C. Sowerby, 1829). Walaszczyk and Cobban, text-figs. 9.3, 25.1, 26.1–26.3, 27.3–27.4, 28.3, 30.2.

Type: By subsequent designation of Woods (1912: 334) the lectotype is BM 43268, being the original of J. de C. Sowerby (1929: pl. 583, fig. 1) from the Upper Chalk, England; the locality is unknown.

Diagnosis: Moderately large for genus, strongly inequivalve; LV coiled, growing moderately obliquely, almost smooth; RV weakly to moderately inflated, ornamented with well-developed rugae.

Material: Twelve specimens in total. Three specimens from Sheep River: TMP 2016.041.0321, TMP 2016.041.0329 and TMP 2016.041.0335, from 143 m. Two specimens from West Thistle Creek: TMP 2016.041.0243 from 72.5 m, and TMP 2016.041.0240 from 100.3 m. Single specimen from Bighorn River, TMP 2016.041.0362 from 51.8 m. Single specimen from Chungo Creek, TMP 2016.041.0188 from 75.7 m. Single specimen from James River, TMP 2016.041.0160 from 80.0 m. Single, unnumbered specimen from Cutpick Creek. Three specimens from Bighorn Dam: TMP 2016.041.0418 from 65.5 m, TMP 2016.041.0423 from 67.5 m, and TMP 2016.041.0431 from 67.5 m.

Measurements: See table 1.

Description: The species is small to medium size for the genus; inequilateral, strongly inequivalve. LV is strongly coiled, up to 1.5 whorls, tightly coiled, in the studied specimens (TMP 2016.041.0243; fig. 12). The LVs grow uniformly at δ = 60°, with strong inflation. The anterior margin gives a more or less consequent plane, and forms a well-developed planispiral coiling. The whorl in cross section is rounded in the lateral, anterior, and posterior parts; the “aperture” is oval. The LV is almost smooth. Only in the juvenile part may irregular, low, rounded rugae occur. Irregular rugae also occur in some specimens in the adult stage, usually at the anterior margin. The RV, when isolated, does not have any characteristic feature that allows it to be identified as belonging to a particular species of Volviceramus.

Remarks: Volviceramus involutus is the only Volviceramus species with almost perfect coiling of the LV, as seen on the anterior wall of the valve, resembling Nautilus or some involute ammonites. The posterior, or lateral (which would be ventral in ammonoids), margin is certainly quite different. The species-level identification of the RV is at the moment impossible. Based on species, of which double-valved specimens are available, the variability of RVs is high, and more double-valved specimens of every species would be necessary to make a reliable assessment.

The infraspecific variability concerns mainly the l/h ratio, which results in more slender or more robust forms. The type species (Sowerby, 1828: pl. 583, figs. 1–3; see also Woods, 1912: text-fig. 88) is one of the robust forms, with high l/h ratio, well above 0.8. The slender form is best represented by Dixon's specimen (1850: pl. 28, fig. 32; see also Woods, 1912, text-fig. 89), with l/h ration about 0.75. The slender form, with Dixon's specimen as its type, was referred by Heinz (1932: 22) to a new species, Volviceramus anglogermanicus. Subsequently, the same specimen was chosen as the type of the new subspecies Inoceramus involutus belovodiensis by Glazunova (1972: 63), with the same diagnosis and the same aim to separate the slender morphotype of Volviceramus involutus. Based on our material it is clear, however, that both morphotypes are extreme variants of the same type and are, consequently, regarded as infraspecific variants (see also Walaszczyk and Cobban, 2006).

The American species Volviceramus umbonatus (Meek and Hayden, 1858) is a typical representative of V. involutus, and consequently is a synonym of Sowerby's species. Volviceramus exogyroides and I. undabundus, which have previously been considered as synonyms of V. involutus, are well defined, separate species (see discussion herein).

Occurrence: Volviceramus involutus first appears in the middle part of the middle Coniacian and ranges into the upper Coniacian. It is well represented in the entire Western Interior Basin. The species is widely known from Europe and western Central Asia. It does not range south into the Mediterranean Province, although it was reported from Gosau in Austria (Tröger and Summesberger, 1994). The reports from Madagascar (Heinz, 1933) and from the western North Pacific Province (Pergament, 1971) have not been confirmed.

1862. Inoceramus exogyroides Meek and Hayden: 26.

1876. Inoceramus exogyroides Meek and Hayden. Meek: 46, pl. 5, fig. 3.

1893. Inoceramus exogyroides Meek and Hayden. Stanton: 83, pl. 17, figs. 1–2 [reillustration of Meek, 1876: pl. 5, fig. 3, specimen]

1898. Inoceramus exogyroides Meek and Hayden. Logan: 454, pl. 88, figs. 1–2 [reillustration of Meek, 1876: pl. 5, fig. 3, specimen].

1907. Inoceramus exogyroides Meek and Hayden. Veatch: pl. 11, fig. 1.

pars 1929. Inoceramus undabundus Meek and Hayden. Heine: 100, pl. 11, fig. 51; pl. 19, fig. 71 [non pl. 11, fig. 50; pl. 13, fig. 57, which are Inoceramus undabundus Meek and Hayden].

1972. Inoceramus obliquus, sp. nov., Glazunova: 63, pl. 8, figs. 2, 3.

2006. Volviceramus exogyroides (Meek and Hayden, 1862). Walaszczyk and Cobban: 291; text-figs. 27.1, 28.1, 29.1, 30.1.

Type: The holotype, by monotypy, is the original of Meek (1876: pl. 5, fig. 3) from the Marias River Shale (Fort Benton Group), 20 miles below “Fort Benton,” on the upper Missouri River, in north-central Montana.

Material: Nineteen specimens. Ten specimens from Bighorn Dam: TMP 2016.041.0404 and TMP 2016.041.0405 from 47.5 m; TMP 2016.041.0414, TMP 2016.041.0415 and TMP 2016.041.0416, from an interval 50–60 m; TMP 2016.041.0417 from 65.6 m; TMP 2016.041.0433 from 67.5 m; TMP 2016.041.0420 from 72.0 m; TMP 2016.041.0441 from 75.4 m; and TMP 2016.041.0438 from 81.0 m. Single specimen from Sheep River, TMP 2016.041.0332 from 110.5 m. Single specimen from West Thistle Creek, TMP 2016.041.0234 from 53.2 m. Four specimens from Chungo Creek: TMP 2016.041.0193, and TMP 2016.041.0194, from 65.8 m; TMP 2016.041.0200 from 65.9 m; and one unnumbered specimen from 65.8 m. Three specimens from Bighorn River: TMP 2016.041.0363, TMP 2016.041.0364, from 51.8 m, and TMP 2016.041.0357, from 93.6 m.

Measurements: See table 1.

Description: The following description refers only to the LV; RVs are not represented in the studied material.

The shell is of small to moderate size, inequilateral. Its outline changes during ontogeny following the change of growth direction; its juvenile outline is triangular, strongly oblique, elongated parallel to the ligament; its adult outline is trapezoidal, due to the change of growth, to distinctly less oblique. The specimens vary between well-geniculated ones (see fig. 13) to forms with a gradual change from the juvenile to adult stage (fig. 14A, B, F, G). The beak is pointed, anteriorly terminal. The umbo is variably coiled, prosogyrate. The change from the oblique juvenile stage to less oblique adult stage is sometimes quite abrupt, geniculated. The juvenile stage is oblique, with δ angle ranging between 30° and 40°; the adult stage growth at δ between 50° and 60°. The outline of the juvenile stage varies with variable inflation; the more inflated specimens have more coiled umbos and are more slender. Depending on the length of the juvenile stage, the adult stage is more or less subquadrate.

The valve is ornamented with regular to subregular commarginal rugae, with regular, ventralward increase of interspaces. The rugae are round topped, symmetrical to slightly asymmetrical. The ornament becomes less distinct in the adult stage, or it disappears completely.

Discussion: Both the original material of Meek and Hayden (1862; also Meek, 1876) and the material recently described from the U.S. Western Interior by Walaszczyk and Cobban (2006) are represented exclusively by LVs. The only reports of the RV come from Europe. These are by Heine (1929) from northern Germany, who referred these forms to Inoceramus undabundus Meek and Hayden; and by Glazunova (1972), who described this species under the new name Inoceramus obliquus (actually, the name is the homonym of v. Haenlein's species). Describing the RV Glazunova (1972) states that the RV is distinctly smaller than the LV and its outline is L-elongated. The beak is pointed, not projecting above the ligament, the umbo is weakly inflated. The valve is more evenly inflated than the LV. The ligamental plate is concave, covered with shallow resilifers intercalated with relatively narrower interresilifers.

Volviceramus exogyroides resembles closely Volviceramus cardinalensis, sp. nov. Both have a distinctly oblique juvenile stage and change to lower obliquity in the adult stage. The juvenile stage of V. cardinalensis, sp. nov., is, however, almost subrectangular, poorly inflated, and almost smooth.

The species has often been placed in synonymy with Volviceramus involutus (or its American synonym, V. umbonatus). Both species differ, however, in their ontogenetic development and consequent morphological characteristics.

The juvenile parts of LVs may easily be taken for a Cremnoceramus. The difference is clearly seen when the ligament plate is preserved, or when the specimen is preserved as with both valves. This may be the reason for reports of Cremnoceramus from the interval characterized otherwise by Volviceramus (see, e.g., Kauffman et al., 1993; Collom, 2001).

Occurrence: Volviceramus exogyroides is known widely in the North American Western Interior. It is also known from Europe, where it was described as Inoceramus obliquus by Glazunova (1972). The species was reported (although without illustration) from the southern and eastern margins of the East European craton (e.g., Aliev and Kharitonov, 1981; Aliev and Pavlova, 1983), but it was never illustrated.

Type Specimens: The holotype is TMP 2016.041.0317, upper middle Coniacian of the Sheep River section; paratypes: 14 specimens from various localities (see Material).

Etymology: After Cardinal River, western Alberta, where one of the paratypes was collected.

Material: Fifteen specimens in total. Four specimens from Bighorn Dam: TMP 2016.041.0399, loose, but located approximately in the interval 50–60 m of the succession, TMP 2016.041.0413 from 43.0 m, TMP 2016.041.0406 from 47.5 m, and TMP 2016.041.0421 from 105.0 m. 10 specimens from Sheep River, from 144 m: TMP 2016.041.0310, TMP 2016.041.0314, TMP 2016.041.0315, TMP 2016.041.0316, TMP 2016.041.0317 (holotype), TMP 2016.041.0318, TMP 2016.041.0319, TMP 2016.041.0320, TMP 2016.041.0322, and TMP 2016.041.0323. Single, double-valved unnumbered specimen from Cardinal River, 96.8 m.

Diagnosis. Noncoiled Volviceramus with LV strongly oblique and weakly inflated in juvenile stage, growing almost orthoclinally, with strong inflation in adult stage. RV strongly inflated for genus, with regular, widely spaced rugae, and shallow radial sulcus on its disc.

Description. The species is strongly inequivalve, noncoiled Volviceramus, attaining large size, with strongly inflated LV up to 30 cm in maximum h length. The LV shows characteristic change in growth direction, leading to the development of the juvenile and adult stages, sometimes, with well-developed geniculation. The juvenile valve, up to 100 mm of axial length, growths obliquely, with δ angle ca. 45°, then, in the adult stage, it changes its growth to markedly less oblique. The juvenile stage is subrectangular in outline, and moderately to weakly inflated. The strong inflation characterizes the adult stage. The adult stage varies in the L/H ratio, ranging from L-elongated, subrectangular specimens to subquadrate ones. The RV is relatively large, with strongly inflated disc, distinctly oblique. The disc is separated from the posterior auricle, along a well-developed auricular sulcus.

The juvenile stage of the LV is almost smooth; the adult stage is covered with subregular, widely spaced, low rugae. The RV is regularly, strongly rugate on the disc; the rugae do not continue over the posterior auricle. The rugae are distinctly narrower than interrugae spaces.

The holotype, TMP 2016.041.0317 (figs. 16, 17), is a huge (estimated maximum h is 180 mm), double-valved specimen, apparently undeformed, with parts of shell in the ligament area preserved. The L of the juvenile stage (fig. 17B) of the LV is ca. 110 mm, and its H is ca. 60 mm. This part is weakly inflated, with juvenile b = 18 mm, smooth, growing moderately obliquely, at δ = 45°. The beak is strongly prosogyrous, curved anteriorly. The α angle is 105°. Although there is no distinct geniculation, at h = 120 mm the valve starts growing perpendicularly to the juvenile stage. The adult stage is subrectangular, longer than high (H is only 110 mm at L = 170 mm).

Remarks. Volviceramus cardinalensis, sp. nov., resembles V. exogyroides. It differs from the latter in its subrectangular juvenile outline, instead of suboval, and lower inflation. Moreover, the juvenile of V. exogyroides is usually regularly rugate, changing to almost smooth in adult stage. In contrary, V. cardinalensis is almost smooth in the juvenile stage, and changes its ornament to distinctly rugate in the adult.

Occurrence: The species seems to appear very low in the middle Coniacian and ranges to the lower upper Coniacian.

pars 2001. Volviceramus involutus (Sowerby, 1828). Collom: 475, pl. 15, figs. 1, 2, 4, 5. [only]

2001. Volviceramus aff. koeneni [in text: Volviceramus koeneni] (Müller, 1888). Collom: 474, pl. 15, fig. 3.

Type Specimens: Holotype is TMP 96.19.13, double valved, moderately large; well preserved (original to Volviceramus involutus (Soweby) in Collom, 2001: pl. 15, figs. 4, 5); paratypes: TMP 2016.041.0439, and TMP 2016.041.0245; both internal molds of LVs, with fragments of shell preserved; moreover: GSC 117324, LV, an original to Volviceramus involutus (Soweby) in Collom 2001: pl. 15, fig. 1; TMP 96.53.1, LV, original to Volviceramus involutus (Soweby) in Collom 2001, pl. 15, fig. 2; and TMP 87.56.13, doublevalved specimen, original to Volviceramus aff. koeneni (Müller) in Collom 2001: pl. 15, fig. 3.

Type Locality: Bad Heart Formation, Kakut Creek (for details of location, see Collom, 2001).

Material: Our material consists of two specimens, both LVs: TMP 2016.041.0439 from Bighorn Dam, 91.5 m; TMP 2016.041.0245 from West Thistle Creek, 107.5 m. Two other specimens, TMP 2016.041.0313 and TMP 2016.041.0326, from Sheep River, are referred to herein as cf. stotti.

Diagnosis: Moderately inflated and moderately inequivalve Volviceramus, of moderate size, rounded, prosocline, with ornament, composed of raised growth lines, with superimposed, low, widely spaced, subregular concentric rugae.

Etymology: After Donald F. Stott, the preeminent Canadian geologist and researcher of the Cretaceous of the Canadian Western Interior.

Measurements: See table 1.

Description: This is a moderately inequivalve Volviceramus species, with both valves regularly inflated, strongly prosocline, straight. LV is larger and more inflated, growing dominantly posteroventrally. The beak is pointed, curved anterodorsally; it projects above the hinge line. The valve outline is parabolical. The anterior margin is relatively short (AM/h between 0.40 and 0.45). The anterior wall is steep to overhanging, rounded. The anteroventral margin is rounded, broadly convex; ventral margin is rounded. The posterior auricle is small, well separated from the disc, particularly in the RV; less so in the LV. The ligament is strong; the resilifers as observed on one of the specimens illustrated in Collom (2001: pl. 15, fig. 1) are narrow and rectangular, with narrow interresilifer plates.

The ornament is composed of regular to subregular, round-edge rugae, superimposed by sharp-edged growth lines, well visible both on outer shell surface and on internal mold.

Remarks: The weak to moderate inequivalveness (the feature inferred from the characteristics of the ligamental plate), moderate to strong inflation of the LV, and a peculiar ornament, make this species different from any other Volviceramus species known. In general architecture V. stotti, sp. nov., resembles V. koeneni, however, the latter is distinctly inequivalve, with RV having a very distinct ornament, composed of sharpedged, strong concentric rugae, with variably developed radial ribs.

Occurrence: The species appears relatively high in the succession, close to the appearance level of Sphenoceramus subcardissoides, which marks the base of the upper Coniacian, and ranges to the top of CA16, in the middle part of the substage.

Material: Two specimens in total, both internal molds of LVs. Single specimen from Sheep River, TMP 2016.041.0334, from 106.5 m; single specimen from Chungo Creek, TMP 2016.041.0195, from 56.9 m.

Measurements: See table 1.

Description: The valves are subrounded to suboval, weakly inequilateral, prosocline, moderately inflated. The beak is pointed, curved strongly dorsoanteriorly. The umbo is subtrigonal. The umbonal part grows obliquely (umbonal δ is between 35° and 40°); then the valve becomes straight, growing at d between 70° and 75°. The posterior auricle apparently does not develop, or is very small (and not preserved on our specimen). The anterior margin is relatively short (AM/h = 0.4); it is concave below the umbo, then straight. The ventral margin is broadly and regularly rounded, long. The posterior margin is not observed on our specimen; it apparently is very short.

The umbonal part is moderately to strongly inflated. The adult stage then becomes weakly or only moderately inflated, and becomes again strongly inflated in the ventral part (?gerontic stage). The valves are almost smooth, or bear only weakly developed, widely spaced, very low rugae; growth lines are not observed.

Remarks: These two specimens resemble closely Volviceramus exogyroides and may easily be imagined as a morphotype of V. exogyroides, which very early in ontogeny changes its juvenile (very oblique) growth to the adult (almost straight). More material is needed to decide whether this morphotype is an extreme variant of V. exogyroides or it is an independent species.

Occurrence: This morphotype is known from only two specimens from our collection. Both are from the lower middle Coniacian (both are from CA7) of Sheep River and Chungo Creek.

Type Species: Inoceramus cardissoides Goldfuss, 1835.

Generic Characters: The genus is obliquely wedge shaped in outline, weakly to moderately inflated, medium to large sized, equivalve and inequilateral. The disc is triangular in outline, with three growth axes (Schalenkante of Seitz: 1965, text-fig. 1), similar to the genus Cordiceramus, commonly with a more or less well-developed radial sulcus in the posterior part of the disc. The umbo is pointed, curved anteriorly, usually extending above the hinge line. The ornament is well developed over the disc, usually much weaker on the posterior auricle. Both concentric and radial ornament elements occur.

Occurrence: Sphenoceramus appeared in the late Coniacian (see Heinz, 1926, 1928; Heine, 1929; Seitz, 1962; Tröger and Christensen, 1991; Walaszczyk and Wood in Niebuhr et al., 1999), and ranged up to the mid early Campanian (Seitz, 1965). It is a Boreal species, rarely reported in the Mediterranean area (see, e.g., Tröger and Summesberger, 1994). The genus seems to be limited to the Northern Hemisphere; reports from the Southern Hemisphere (Heinz, 1929; Kauffman in Kennedy et al., 1973) are not confirmed (see discussion in Walaszczyk and Cobban, 2006; Kennedy et al., 2008; Walaszczyk et al., 2014a). The genus is widely reported from the North Pacific Province, particularly from its western parts. How abundant the genus was in this province is, however, unclear. Of a wide variety of morphotypes referred to Sphenoceramus (e.g., Matsumoto et al., 1982; Toshimitsu, 1988; Noda, 1988), most should be referred to other genera (e.g., Glazunov, 1976; Zonova, 1992, 1993).

In the Western Interior Basin Sphenoceramus occurs regularly only in its northern part; probably ranging south to Montana. Further south the genus appears sporadically.

1877. Inoceramus subcardissoides Schlüter: 271, pl. 37

1905. Inoceramus subcardissoides Schlüter. Wegner: 169

1926. Inoceramus subcardissoides Schlüter. Heinz: 101

1932. Inoceramus subcardissoides Schlüter. Heinz: 24.

1953. Inoceramus subcardissoides Schlüter. Odum: 12

1956. Inoceramus ex gr. subcardissoides Schlüter. Soukup: pl. 13, figs. 1–3.

1958. Inoceramus subcardissoides Schlüter. Kotsubinsky: 16, pl. 5, fig. 24.

1968. Inoceramus subcardissoides Schlüter. Kotsubinsky: 137, pl. 24, fig. 3.

non 1969. Inoceramus subcardissoides soukupi Mitura in Mitura et al.: 175, pl. 2, fig. 1

1974. Inoceramus cf. subcardissoides Schlüter. Tröger: pl. 6, figs. X4307, 4308

1991. Inoceramus subcardissoides Schlüter. Tröger and Christensen: 32, pl. 2, fig. 4.

pars 2001. Euryceramus cardissoides (Goldfuss). Collom: 489, pl. 13, fig. 5; pl. 14, figs. 1–2 [non pl. 13, fig. 6]

Lectotype: The original to Schlüter (1877: pl. 37), from the Emchermergel of the rock-waste deposit of the Carnap I Mine Shaft near Horst in Westphalia, northern Germany.

Material: Seven specimens in total. Two fragments, TMP 2016.041.0443 from 92.5 m and TMP 2016.041.0444 from 92.0 m from Bighorn Dam. One fragmentary specimen, TMP 2016.041.0235 from 100.3 m in West Thistle Creek. Incomplete huge specimen TMP 2016.041.0201 from 96.5 m in Chungo Creek. One large incomplete specimen (internal and outer mold of the same), TMP 2016.041.0001, and TMP 2016.041.0002, from 132 m of Ram River. Incomplete fragment, TMP 2016.041.0338 from Sheep River.

Description: The best preserved is TMP 2016.041.0001 (fig. 21), the large fragmentary specimen from the Ram River section (and TMP 2016.041.0002, its outer mold). It is the medium stage part of the RV, with h =190 mm. Its juvenile and the anterior parts are missing. Also, it is slightly deformed in the preserved anterior part. The disc is wide, moderately inflated, apparently triangular in outline, covered with widely spaced, round-topped rugae and strong radial ribs. The latter weaken when crossing concentric rugae to form weakly developed nodes. The specimen retained a well-preserved radial sulcus, which is relatively broad and deep in the posterior part of the disc. The posterior auricle is not preserved. The radial ornament disappears from the radial sulcus, and reappears on the disc, posterior to the sulcus.

TMP 2016.041.0235, from Thistle Creek, represents a much younger stage of the LV. It shows well, however, the tripartite disc and, although weak, clearly developed radial ribs.

TMP 2016.041.0444, from Bighorn Dam, is a juvenile stage, 75 mm h long fragment. The specimen does not have radial ornament yet, which appears later in ontogeny. The outline and structure of the disc fits the characteristics of the species.

Discussion: Although incomplete, our specimens show well the characteristics of Schlüter's species: the presence of the strong, broad radial sulcus in the posterior part of the disc and the radial ornament, which crosses the concentric rugae, forming more or less well-developed nodes at crossings.

The best reported specimens, besides the illustrated type, are the ones photographed by Collom (2001: pl. 13, fig. 5; pl. 14), from the upper Coniacian of the Smoky River area. His specimen from the Puskwaskau Formation (Collom, 2001: pl. 13, fig. 6) has different ornament and character of the posterior auricle, and is a different species.

Occurrence: Sphenoceramus subcardissoides first appears apparently at the base of the upper Coniacian (Tröger, 1989; Tröger and Christensen, 1991; Walaszczyk and Wood in Niebuhr et al., 1999). Heinz (1926) and Kotsubinsky (1958, 1968) reported the species from the upper Coniacian (upper Involutus Schichten in Heinz, 1926). Although quoted sometimes as ranging into the Santonian; no definite occurrence from this level can be confirmed. Consequently, it may be regarded as of late Coniacian age. In the studied area the species is common at the base of its range; its record higher in the succession is poorly known.

2006. Sphenoceramus ex gr. pachti (Arkhangelsky, 1912). Walaszczyk and Cobban: textfigs. 48.7, 48.10, 48.11.

Material: Three specimens from Cripple Creek: TMP 2016.041.0152, TMP 2016.041.0153, and TMP 2016.041.0154. Twenty-six specimens from West Thistle Creek; TMP 2016.041.0246-TMP 2016.041.0271. Two specimens from Bighorn Dam, TMP 2016.041.0424 and TMP 2016.041.0430. Numerous uncataloged specimens from Cardinal River.

Description: The species is small to medium size for the genus, inequilateral, apparently equivalve (?semiequivalve). The valve is weakly to moderately inflated, unless geniculated, quite oblique, with d between 45° and 50°. The valve outline is trapezoidal. The disc is trigonal in outline. The posterior auricle is usually well developed and well separated from the disc. The distinct auricular sulcus is visible in some specimens. The very distinct radial sulcus runs posteriorly of the growth axis. It starts at ca. 10 mm from the beak and becomes stronger with age. The beak is pointed, curved anterodorsally, projects slightly above the hinge line. The anterior margin is relatively short, usually slightly above 50% of the growth axis length, quite steep, may be slightly concave just below the umbo. The anterior margin passes into the long, broadly convex anteroventral margin. The ventral margin is narrowly rounded. The posterior margin is straight, almost parallel to the growth axis, being about 60% of the growth-axis length. The growth axis is straight in the juvenile and early adult part, then curves posteriorly. The ligament (dorsal) margin straight, relatively short, below 50% of the respective growth-axis length.

The general outline and shape changes in geniculated specimens. The geniculation appears usually at between 30 and 40 mm axial distance from the beak. The geniculation angle varies but is approximately 60°. Rarely, double geniculation is observed. The geniculated forms are character- ized by a steep (sometimes overhanging) anterior wall, and sharp anterior margin (fig. 22J).

The ornament is composed exclusively of commarginal rugae; very fine, discontinuous radial elements appear on some specimens (TMP 2016.041.0152, fig. 23D). Up to 20 mm of the axial length the rugae are poorly developed, and the ornament is composed almost entirely of raised, sharp-edged growth lines. In some specimens the rugae appear, however, much earlier, and the growth lines are poorly visible. In most of the specimens the rugae show a distinct stepwise change from rather closely spaced, roundtopped ones, to widely spaced ones, with distinctly sharper edges. In the geniculated specimens, the change is associated with the change of growth plane. The growth lines become less and less regular with age. The rugae do not pass onto the posterior auricle. In the geniculated specimens they pass onto the anterior wall.

Remarks: The studied material looks at first very variable. To a large extent this is, however, because of the genicution; the geniculation causes changes in the character of the anterior margin and wall, and in the general shape of the whole specimens. Other than that, the specimens are quite stable with respect to general outline and ornament.

The general outline, ornament and ontogenetic changes make our specimens clearly representative of Sphenoceramus pachti. The difference between the Arkhangelsky's types and the studied material is the lack of radial ornament. In this respect, our specimens correspond to S. pachti subsp. indet. as described by Seitz (1965: pl. 9, figs. ?1, 3–4). Seitz suggested the possibility that his undescribed variety could represent juveniles of otherwise typical (i.e., radially ornamented) S. pachti. Although this is also possible in the case of our material, no radially ribbed specimen of S. pachti has ever been reported from the Western Interior Basin, and our material also seems to include adult specimens. Consequently, our specimens are regarded as representing a sample of a nonradially ribbed natural population.

The geniculated, and particularly the smallsized specimens of S. pachti described herein very closely resemble the type of I. pontoni McLearn (1926: pl. 20, fig. 1). The only differences that may be indicated, based on the limited material of McLearn's species, are: (1) weakening of the posterior radial sulcus and (2) general weakening of the ornament in the adult stages of I. pontoni (this is not the case in S. pachti). The typical specimens of McLearn's species, collected from the Smoky River area, western-central Alberta, and from the Kevin section, northern Montana, come from beds slightly younger than S. pachti. Consequently, it is suggested herein that I. pontoni may represent an evolutionary descendant of S. ex gr. pachti.

Occurrence: The material studied is from the lower Santonian of Alberta, Canada. Very similar specimens occur higher in the lower and middle? Santonian.

1965. Inoceramus cardissoides subsp. indet. Seitz: 47, pl. 4, figs. 1–4.

2006. Sphenoceramus ex gr. cardissoides (Goldfuss, 1835). Walaszczyk and Cobban: textfigs. 48.3–48.6.

Material: Single RV, RTM 2016.041.0272, from 126 m level of West Thistle Creek.

Description: The studied specimen (fig. 24) is the small-sized internal mold of the RV; its hmax = 48.5. The valve is strongly inflated as for S. cardissoides; its b/h= 0.45. The disc is subquadrate in outline, prosogyrate. The beak is pointed, curved anterodorsally, projecting above the hinge line. Its anterior margin is distinctly concave, relatively long, with AM/h = 0.65, which is distinctly higher than in S. ex gr. pachti (ca. 0.5 or less). The anterior wall is steep to overhanging. The ventral margin is rounded. The radial sulcus is well developed. The posterior auricle is not preserved.

The valve is ornamented with strong commarginal rugae, sharp-edged, with flat, and relatively large interspaces. The rugae are superimposed by raised, sharp-edged growth lines. Traces of weak radial ribs are visible in the axial part of the valve.

Remarks: The specimen clearly belongs to the Sphenoceramus pachti-cardissoides group. Its relatively long anterior margin is a characteristic of S. cardissoides. The lack of radial ornament makes it close to forms referred by Seitz (1965: 47) to Inoceramus cardissoides subsp. indet. Similarly, as with nonradially ribbed variety of S. pachti, Seitz did not name this variety, suggesting that it might comprise only the juvenile stages of other, radially ribbed species. The presence of this morphotype in the U.S. Western Interior suggests that the variety may represent a separate taxon.

Occurrence: The studied specimen comes from the lower Santonian of the West Thistle Creek section; the US Western Interior specimens come from the Santonian. The morphotype is also known from the lower and middle Santonian of Germany (Seitz, 1965).