Horizon and locality: Linton, Ohio, Coal Measures.
The best preserved example of this species includes 9 vertebræ and the corresponding ventral armature. The centra, seen from below, are much contracted in their form, presenting an obtuse median rib, which expands to the articular extremities. In one or two instances the latter are divided by fracture, and the moderately concave form of the adjacent surfaces is displayed. The diapophyses are of complex form, but the details are concealed by the prevalent thin layer of coal which invests them. An inferior prominence runs parallel to the centrum; outside of this the process is obscurely trilobate and thickened, not flattened, as in the caudal vertebræ of Ptyonius. Several ribs ([fig. 8]) of moderate thickness appear by the side of the diapophyses. Eleven abdominal ribs in 5 mm.
The second specimen was originally referred to Œstocephalus remex, as a posterior portion of its vertebral column, immediately preceding the caudal series.
This reference appears to be incorrect, although the resemblance between the corresponding parts in the two genera is no doubt considerable, and the alternative of proposing a new genus and species was not at that time advisable.
The neural spines are longer than high, and are nearly in contact at their margins; each is marked by about 5 obtuse vertical ribs. A fractured section of the abdominal spines in place displayed at least six layers of them.
The material on which the above account is based is imperfect. The specimen figured by Cope (Geol. Surv. Ohio, vol. II, pt. II, pl. xxxi, fig. 2, 1875) is undoubtedly a portion of the vertebral column of Œstocephalus remex. Nos. 4462 and 4480 of the United States National Museum may be representatives of Thyrsidium fasciculare, but they are more probably Œstocephalus remex; if they are the latter this leaves the type as the only known specimen of the species.
| Measurements of Type of Thyrsidium fasciculare Cope. | |
| mm. | |
| Length of portion of vertebral column preserved | 7 |
| Width of ventral armature | 18 |
| Length of a vertebra | 9 |
| Width of same vertebra | 4 |