The genus finds its nearest allies in the forms of the species of the genus _Sauropleura_, in which Cope formerly located the present species. The skull of the form described as _Tuditanus radiatus_ Cope is quite similar to the present form, both in the sculpturing and arrangement of the elements. The characters wherein the present form resembles the species of _Sauropleura_ are the possession of broad pectoral plates and strong, digitate limbs. The general form of the body and skull is different in the two groups. It is slender in _Sauropleura_ and decidedly stout, short, and heavy in Saurerpeton. Measurements of the Type. mm. Length of specimen 130 Median length of skull 51 Width of skull at posterior border 62 Width of skull across orbits 48 Length of orbit 14 Width of orbit 10 Interorbital space 16 Length of longest tooth preserve 14 Length of shortest tooth preserved 1 Length of the interclavicle 26 Width of interclavicle, maximum 23 Length of clavicle 22 Width of clavicle 18 Length of abdominal scutes 28 Length of humerus 19 Width of humerus at upper end 6.5 Length of ulna 11 Length of radius 9 Length of metacarpal 3 Length of first digit 12 Length of terminal phalanx 3.5 Length of lower jaw on the curve 70 Width of lower jaw, maximum 8 Length of rib 30 =Genus CTENERPETON Cope, 1897.= Cope, Proc. Am. Phil. Soc., XXXVI, p. 83, pl. iii, fig. 1, 1897. Type: _Ctenerpeton alveolatum_ Cope. The genus _Ctenerpeton_ was founded by Cope for the reception of a single species which presents some very unusual characters. The form shows close relationships to the genera _Urocordylus_ (334), _Œstocephalus_, and _Ptyonius_. These genera agree with the present one in the possession of very characteristic vertebræ which are signalized by the elongate and ornamented characters of the neural and hæmal spines. These project prominently from the body of the vertebra and have the ends of the projections truncate and divided into fine points, thus causing the spine to have much the appearance of a comb. The surface of the neural spine is sometimes marked with a shallow groove. The spines are longer and more slender in the genera _Œstocephalus_, _Urocordylus_, and _Ctenerpeton_ than they are in the species of the genus _Ptyonius_, where they are short, although the usual pectinations are present.