Characteristic of the species are the remarkable length and slenderness of the fan-shaped neural and hæmal spines, and the absence of an acute serration on their margins. In this species the spines have a laminiform expansion at the base in their plane. One specimen exhibits the pelvic region, including a portion of the tail. The ilium has an expanded anterior extremity and is directed backwards and somewhat inwards on either side of the vertebral column. The femur is nearly straight, short, contracted medially, and expanded distally. The tibia is shorter and is subcylindrical. Beneath the ilium the last chevron of the abdominal rods appears, the outer extremities rising on the base of the tail.
The pectoral arch is almost unknown, and Cope based the distinction of Ptyonius, and Œstocephalus on the absence of these plates in the latter genus an uncertain characterization. The fore limbs are indicated by a humerus. There were possibly from 75 to 100 vertebræ in the entire column. The animal was exclusively adapted to life in the water and was, without doubt, an excellent swimmer. There are preserved in one specimen portions of what seem to be hyobranchial elements.
| Measurements of Œstocephalus remex Cope. | |
| mm. | |
| Length of entire caudal series | 195 |
| Width at ninth vertebra | 21 |
| Width at thirty-sixth vertebra | 2 |
| Length of four phalanges in place | 14 |
| Expanse of fan of proximal caudal | 18.5 |
| Length of ilium | 11.5 |
| Length of femur | 11.5 |
| Length of tibia | 7 |
| Length of mandibular dental series | 24 |
| Depth of mandible at middle | 5 |
| Nine teeth in | 5 |
| Length of longer teeth | 2 |
| Length of first hæmal branchial | 6 |
| Length of sixth vertebra from skull | 7 |
| Width of centrum | 3 |
Œstocephalus rectidens Cope.
Cope, Trans. Amer. Phil. Soc., p. 268, Apr., 1874.
Cope, Geol. Surv. Ohio, II, pt. II, p. 386, pl. xxvii, fig. 3, 1875.
Type: Specimen No. 9033, American Museum of Natural History, collection of J. S. Newberry.
Horizon and locality: Linton, Ohio, Coal Measures.
The species is indicated by a left dentary bone, with its teeth and external surface preserved. The latter is nearly smooth and without sculpture. The outer face is convex, and the general form is slender, but not curved upward at the extremity. The extremity of the dentary does not show any evidences of teeth. Teeth straight and conic, apex acute, non-plicated.
Cope also associated with this species a portion of a caudal series, consisting of 25 vertebræ. The centra are elongate and expanded at the extremities. The neural arches have a close union. The neural and hæmal spines are fan-shaped and striated. The bases are quite narrow.