Our knowledge of the genus is confined to the skull. The genus was established for certain members of the genus Tuditanus and other forms which have been recently described. The species of the genus are: _E. radiatus_ Cope type, _E. tabulatus_ Cope, _E. tuberculatus_ Moodie, _E. obtusus_ Cope, _E. minutus_ Moodie, _E. acutirostris_ Moodie, _E. sculptilis_ Moodie. All of the species are from the Linton, Ohio, Coal Measures, with the exception of _E. sculptilis_ and _E. minutus_, which are from the Cannelton, Pennsylvania, slates. The position of the genus as to family is a little uncertain, since family characters are not yet well understood among the Carboniferous forms on account of the lack of information as to the structure of the animals. If we take the absence of the ventral scutellæ as a family character, the genus will be in the family Tuditanidæ, but the evidence on this point is negative. For the present we may place the genus only provisionally in the family Tuditanidæ. The arrangement will undoubtedly require revision later. =Erpetosaurus radiatus Cope, 1874.= Cope, Trans. Amer. Phil. Soc., XV, p. 273, 1874. Cope, Geol. Surv. Ohio, II, pt. II, pp. 394-395, pl. xxvii, fig. 1; pl. xxxiv, fig. 3; text-fig. 10, 1875. Moodie, Bull. Amer. Mus. Nat. Hist., XXVI, p. 348, pl. lxii, fig. 1, 1909. Type: Specimen No. 8600 G, American Museum of Natural History. Locality and horizon: Linton, Ohio, Coal Measures. (Plate 25, fig. 1.) Cope originally described this species from a portion of a skull. He (123) characterized the form as follows: "The marked character of this form is seen in the very anterior position of the orbits and the contraction of the muzzle. The orbits are large and are separated by a little more than their own diameter; their posterior border is in front of a line measuring the anterior third of the length to the supraoccipital crest, and nearly to the line marking the fourth of the length to the quadrate region. The posterior outline of the skull is deeply concave, the quadrate angle projecting beyond the occipital condyles." The base of the specimen is broken and there is no place for the occipital condyles. Unless the specimen has been mutilated since Cope studied it, the occipital condyles are not present. The restoration of the skull given in figure 22, B varies but little from that given by Cope in 1875. The elements are practically as he represented them.