The character on which this genus rests is the shelf-like extension (plate 23, fig. 2) of the abdominal plates. This is of a very unusual character and entirely unknown in any other species of Carboniferous Amphibia. The term Ctenerpeton has reference to the fact that the ends of these shelf-like plates project in a pectination along the side of the abdomen. =Ctenerpeton alveolatum Cope.= Cope, Proc. Am. Phil. Soc., XXXVI, p. 83, pl. iii, fig. 1, 1897. Moodie, Proc. U. S. Nat. Mus., 37, p. 24, pl. 10, 1909. Type: Specimen No. 4475, U. S. National Museum, Lacoe Collection. Horizon and locality: Linton, Ohio, Coal Measures. The species rests on a single specimen (plate 19) from Linton, Ohio, and is preserved on a block of bituminous coal. It is in a very good state of preservation. There are present on the block of coal a part of the right fore limb, the greater part of the dorsal portion of the animal, and the anterior part of the tail. There are no evidences of hind limbs, although this may not be taken as evidence that they were not present on the animal. No thoracic plates have been observed. The chevron armature is present beyond the cloacal region, but there are no evidences of the specialized clasping organs which are apparently developed from the abdominal armature in some forms (251). Each dermosseous rod of the abdominal scutellation consists of three pieces a median angulated portion and the two lateral parts which form the shelf-like projection along the side of the abdomen (plate 23, fig. 2). The marginal chevron differs in form from the other plate, aside from the fact that it is not angulated. The lateral shelf is composed of flattened plates which articulate with the median piece, and at the place of articulation there is a ridge present in the specimen. The exterior plates are curved backwards and are somewhat attenuated distally. They are broader than the median piece and differ also in the absence of the characteristic alveoli. The median plate is angulated and is of more slender proportions than the lateral pieces. Its ventral surface is ornamented with a single row of closely placed alveoli which resemble in a great degree the alveoli of the jaw of some small animal. The ventral scutellation is broad anteriorly, but becomes more slender posteriorly and shortly posterior to the cloacal region disappears. [Illustration: MOODIE PLATE 23 1. Left leg and pelvis of _Ichthycanthus platypus_ Cope, from the Coal Measures of Ohio. × 1.7. Original the property of the Department of Geology of Columbia University. _c_=centrale; _F_=fibula; _fi_=fibulare; _Fe_=femur; _i_=intermedium; _Il_=ilium; _T_=tibia; _t, 1-5_=distal tarsalia; _ti_=tibiale; _V_=caudal vertebræ; _I-V_=digits. 2. Ventral scutellæ of _Ctenerpeton alveolatum_ Cope, from the Coal Measures of Ohio. × 3.5. Original in U. S. National Museum. ]