The genus was proposed for the reception of a single species originally referred by Cope to _Ceraterpeton_ (_C. tenuicorne_). The species can not be placed in the genus Ceraterpeton on account of the form and structure of the skull, which varies widely from that of the type species, Ceraterpeton galvani Huxley, from the Kilkenny Coal Measures of Ireland. The most important character in which the present species differs from _C. galvani_ is the peculiar form taken by the squamosal and by the position of the "horn." These characters will be evident on referring to figure 25. No undoubted remains of _Ceraterpeton_ have been found outside the British Isles. Fritsch referred (251) a species, previously described as _Scincosaurus crassus_, to this genus, but Andrews (8), Jaekel (347) and Woodward (630) all unite in placing the species in the genus where it was formerly described. Jaekel even says that the Scincosaurus has no horns, so far as he can determine. Cope referred 3 species (123) from the Linton Coal Measures of Ohio to the genus _Ceraterpeton_, but it has been shown elsewhere (347) that no one of them belongs in the genus, nor in fact do they all belong in one genus. =Eoserpeton tenuicorne Cope.= Cope, Geol. Surv. Ohio, II, pt. II, pp. 372-373, pl. xlii, fig. 2, 1875. Cope, Proc. Am. Phil. Soc., XXII, p. 407, 1885. Cope, Proc. Am. Phil. Soc., XXXVI, p. 85, pl. iii, fig. 2, 1897. Moodie, Proc. U. S. Nat. Mus., vol. 37, p. 23, 1909. Type: Specimen in the American Museum of Natural History. There are also specimens Nos. 4472 and 4473 in the U. S. National Museum. Locality and horizon: Linton, Ohio, Coal Measures. The species was founded on a complete skull preserved on obverse sides of a block of coal. Cope (123, pl. XLII, fig. 2) figured this skull. The figure is poorly executed and does not do justice to the specimen, which is really well preserved. In general the skull is oval, with the orbits located well towards the acuminate snout. The interorbital space is equal to twice the width of the orbit. The pineal foramen lies near the center of the skull. The quadrate angles are drawn out into slender acuminate, longitudinally striate horns, processes from the squamosal. The "horn" arises from an expanded base, which is a portion of the cranial element at the postero-lateral angle of the skull. This character is taken as the distinctive one of the genus. It is possessed by no other form of Carboniferous air-breathing vertebrate, in association with the other characters of the form. Measurements of the Type of Eoserpeton tenuicorne.