This species is based on a fragmentary cranium (plate 26, fig. 1) consisting of the posterior part of the right side of the skull. Its association in the genus is solely on the character of the sculpturing of the cranial elements. It is most closely related, in the characters preserved, to the form described by Cope as _Tuditanus radiatus_, from which it differs especially in the character of the sculpture and in the position of the orbits, as well as the arrangement and size of the various cranial elements, so far as these elements can be detected in the present specimen. In _Erpetosaurus radiatus_ the skull is sculptured by radiating grooves and ridges which did not arise from a definite center. In _E. tuberculatus_ this center of radiation is marked by an elevation or tubercle on each cranial element exposed, from which the grooves and ridges radiate outward. These tubercles have an elevation of 4 mm. above the cranial element proper. The orbit is located near the median line of the skull, so far as can be determined. In _E. radiatus_ Cope the orbits are located well forward. In that species also the postparietal is smaller than in the present species and the squamosal is longer and more slender. (Plate 25, fig. 1.) The fragment of a skull on which the above comparison has been made consists of the right postparietal, a portion of the tabulare, the parietal, the frontal, and a portion of the squamosal. The other elements are not clear. The elements in the median line are elongate, as in _Erpetosaurus radiatus_. The pineal foramen is located well back on the median line and lies posterior to two-thirds of the length of the parietals. The sutures separating the frontal and parietal elements from each other in the median line are of the zigzag form so characteristic of the labyrinthodonts. Measurements of the Type of Erpetosaurus tuberculatus Moodie. mm. Length of portion of skull preserved 52 Width across tabulare (estimated) 60 Length of parietal 15 Maximum width of parietal 11 Length of frontal 22 Width of frontal 12 =Genus ODONTERPETON Moodie.= Moodie, Proc. U. S. Nat. Mus., 37, p. 19, 1909. Type: _Odonterpeton triangularis_ Moodie. The generic characters may be found in the triangular shape of the skull, the large size of the teeth, the shape of the vertebræ, the small size of the orbits, and their anterior position as shown in the type specimen (fig. 22, E). The name of the genus is derived from the remarkable size of the teeth as compared with the size of the skull. =Odonterpeton triangularis Moodie.= Moodie, Proc. U. S. Nat. Mus., 37, p. 19, pl. 6, fig. 3, 1909. Type: Specimen No. 4465, U. S. National Museum. Horizon and locality: Linton, Ohio, Coal Measures.