Locality and horizon: Coal Measures of Kilkenny, Ireland.
Stout and long-tailed forms, with the tabulare cornua frequently much produced and pitted cranial bones; lateral lines well-developed; palate with teeth on palatines, vomers, premaxillæ, and maxillæ, the two latter elements bearing conical teeth and the others bearing short, stumpy cones, at least in one species; pineal foramen well forward; nostrils and orbits in the anterior part of skull; scapula peculiarly curved and pointed; other pectoral elements sculptured; neural spines and chevrons of caudal vertebræ much dilated at their extremities, and pectinated; no caudal ribs; vertebræ in one genus apparently capped with a sculptured plate as in Zatrachys; tail very long and tapering to a point, 50 to So caudal vertebræ; dorsal region short; limbs well developed, with clawed digits; carpus and tarsus cartilaginous; endochondrium well formed.
There are 4 genera which constitute this family: Urocordylus, from the Coal Measures of Ireland; Ceraterpeton, from the Coal Measures of Ireland and England; Diceratosaurus, from the Coal Measures of Linton, Ohio; Eoserpeton, from the Coal Measures of Linton, Ohio.
These may be distinguished by the following characters:
| I. | Skull triangular, truncated behind, with rounded muzzle and aborted tabulare cornua, neural spines of caudal vertebræ long, slender, and expanded in a fan-like manner; tail with about 80 vertebræ; ventral scutes oat-like | [Urocordylus.] |
| II. | Skull parabolic and of great width, with short cornua projecting from the supratemporal; tabulare cornua nearly twice as long; neural spines of caudal vertebræ low and wide; ventral scutes oblong; caudal vertebræ about 50 | [Ceraterpeton.] |
| III. | Skull broad with obtuse snout, tabulare cornua absent, large, pointed posterior expansions from supratemporal, posterior table within the cornua truncate; vertebræ with an apical sculptured plate; caudal vertebræ numerous, over 75; ventral scutellæ bristle-like, arranged en chevron | [Diceratosaurus.] |
| IV. | Skull a broad oval, with large posterior projecting supratemporal horns, posterior table of skull between cornua truncate without the small lateral projection from the supratemporal, orbits a long oval, ribs long, curved and slender, tail unknown, possibly shorter than in other members of the family; it is restored as short in Journal of Geology, XVII, p. 77, fig. 20, 1909, but this is uncertain; the skull has all the characters of the family | [Eoserpeton.] |
The relationships of the family are not far to seek. They fall in immediately with the Amphibamidæ and Hylonomidæ in being among the most reptile-like of the Paleozoic Amphibia. The group is, however, distinctly amphibian in the possession of 4 fingers, with the usual microsaurian phalangeal formula.
Genus DICERATOSAURUS Jaekel, 1903.
Jaekel, Neues Jahrbuch f. Mineral., Geol. u. Paleon., Bd. 1, p. 112, 1903.
Moodie, Jour. Geol., XVII, pp. 63-69, figs. 13-15, 1909.
Type: Diceratosaurus punctolineatus Jaekel.