| Measurements of the Type. | |
| mm. | |
| Length of specimen | 32 |
| Length of skull | 12 |
| Posterior width of skull | 11 |
| Length of premaxilla | 5 |
| Length of mandible | 10 |
| Length of axialhyal | 3 |
| Length of postbranchial | 4 |
| Width of vertebra | 1 |
| Length of vertebra | 3 |
| Length of rib | 6 |
The other specimen of this species ([fig. 16a]) is interesting in having 40 consecutive vertebræ preserved, and 19 pairs of ribs attached in their natural relations to the skull and hyal elements. There are a few hyal elements preserved, but nothing is added to our previous knowledge. The ribs are quite as in the type specimen, as are also the vertebræ. The animal was apparently a slender, eel-shaped amphibian comparing favorably with the modern Amphiuma in this respect. There are no indications of limbs or limb girdles.
Fig. 16a. Nearly complete specimen of Cocytinus gyrinoides Cope, from the Coal Measures of Linton, Ohio. Original in the American Museum of Natural History. × 0.95.
| Measurements (No. 2564, American Museum of Natural History). | |
| mm. | |
| Length of entire specimen | 113 |
| Length of skull | 15 |
| Width of head posterior | 15.5 |
| Length of vertebra | 2 |
| Length of rib | 4 |
Moodie, Kans. Univ. Sci. Bull., VI, No. 2, p. 328, 1912.
Type: Erierpeton branchialis Moodie.
The generic characters are found, first of all, in the presence of hyobranchial arches which indicate its relationship to the formerly described Cocytinus gyrinoides Cope, from Ohio. The only other known extinct genera of Caudata which possess, or at least have preserved, the hyobranchial arches are the Jurassic Hylæobatrachus from Belgium and Lysorophus from the Permian of Texas. The present form is widely distinct from both of these genera in the shape of the mandible and the form and arrangement of the hyobranchial bars. The genus Erierpeton finds its closest ally in Cocytinus, in the family Cocytinidæ, which possibly belongs in the order Caudata and the suborder Proteida of Cope.