Species: Beloitoceras amoenum (Miller, 1879)
Formerly: Cyrtoceras amoenum
Map point data provided by iDigBio.
- C6 Sequence (Elkhorn, Upper Whitewater)
- C5 Sequence (Saluda)
Identification in Hand Sample
- Compressed shells that reach maxiumum diameter toward apex of body chamber
- Straight dorsum
- A relatively large, elongate, and slender species
- Sutures become strongly oblique with ontogeny
- Ventrally located siphuncle with narrow segments
Beloitoceras amoenum from Whitewater formation of Butler County, Ohio (CMCIP 24417)
- Beloitoceras amoenum is most similar to B. cumingsi Flower, from equivalent fine-grained limestones of the Saluda Formation in southeastern Indiana and adjacent portions of western Ohio. Both species have adorally compressed shells that have their maximum diameter just adapical of the body chamber, straight dorsums, and sutures that slope adorally from the dorsum to the venter. Beloitoceras cumingsi differs from B. amoenum in being a smaller, more rapidly expanding shell.
Pojeta Jr. (1983):
- Relatively large, elongate, slender species of Beloitoceras, the greatest shell diameter just adapical of the body chamber, an essentially straight dorsum, and sutures that, with ontogeny, become strongly oblique, sloping adorally from the dorsum to the venter.
- Size large for genus (estimated lengths up to 12.0 cm and observed shell diameters up to 3.8 cm); rapidly expanding (apical angle 22-26 degrees), exogastric brevicones whose dorsal outline is concave adapically, becoming nearly straight or slightly convex with ontogeny, having the maximum shell diameter just adapical of body chamber. Venter broadly convex for the length of the shell. Shell cross section ovate adapically, becoming more compressed adorally with ontogeny. Sutures straight, transverse adapically, becoming strongly oblique with ontogeny, sloping adorally from the dorsum to the venter. Cameral chambers short, cameral length decreasing with ontogeny from one-sixth to one-ninth the diameter of the shell at diameters of 15-25 mm, then increasing adorally from one-ninth to one-seventh the diameter of the shell at diameters greater than 25 mm. Adoralmost septa becoming approximate in larger specimens, cameral lengths reduced to one-twentieth the diameter of the shell. Body chamber short, one-fifth the total length of the shell, highly compressed, tapering toward aperture. Aperture marked by well-developed ventral hyponomic sinus and shallow dorsal sinus. Shell exterior marked by coarse tranverse lirae.
- Siphuncle located at ventral margin. Segments narrow, diameters one-eighth to one-ninth the diameter of the shell; slightly expanded, depressed ovate in outline. Structure of septal necks and connecting rings unknown.
- This is a relatively large Beloitoceras of somewhat variable proportions, the known representatives of which show variation in rate of expansion, depth of camerae, form of dorsal profile, and length of living chamber. Distortion is sufficiently widespread in specimens of this form to make it uncertain how much of the variation is natural.
- The holotype (Univ. of Cincinnati, No. 106) presents one well-preserved lateral surface, the opposite side being poorly preserved adorally and missing adapically. The shell has a maximum length of 86 mm. The venter was apparently uniformly convex, with a radius of curvature of 65 mm. The dorsum is faintly concave. The height of the shell increases from 23 mm. to 29 mm. in the basal 30 mm. on the venter and a dorsal length of 28 mm.; in the remaining 50 mm. of the phragmocone the height increases to 33 mm. parallel to the septum at the base of the living chamber. The living chamber has a maximum length of 28 mm. laterally, but is apparently incomplete adorally, and it is not certain that even where it is longest that the aperture is attained. The greatest height of the shell is attained 20 mm. apicad of the base of the living chamber. There the shell height is 35 mm. The sutures slope increasingly orad from dorsum to venter as they are traced adorally, but do not develop conspicuous lateral lobes. The camerae increase gradually in depth from the apex, where four occur in a length of 10 mm., to the adoral part of the shell where four occur in a length of 18 mm. The last five camerae are gerontically shortened, occupying a length of 9.5 mm. Siphuncle and surface marking are not preserved. The width of the shell is 30 mm. where the height is 34 mm. It is not certain that even here there may be slight compresstion.