The vertebræ are short, with expanded neural and hæmal spines. The expanded condition of the neural spines begins over the thoracic region, where they are low. They become well developed in the posterior dorsal region. The caudal fan-shaped spines are larger. The dilated portions form equilateral triangles which stand on moderately short pedicels. They are weakly ridged, and each ridge is prolonged into a narrow acute tooth beyond the margin, 11 of which may be counted on one of the best preserved spines. The longitudinal striæ are terminated near the pedicel by two others which cross obliquely from each side, and, meeting, present the appearance of the margin of a cup sculptured in relief, from which the striæ arise. Pedicels smooth. The spines are in contact at their angles, thus forming a continuous line. In a typical specimen there are 6 in half an inch, in another 7, and in a third 8. The ribs are well-developed and slender. No traces of fore limbs have been detected in the numerous specimens, but elements of hind limbs are preserved. In one of these the femur is a small bone, contracted at the middle. The form of the body is snake-like. There were probably from 75 to 100 vertebræ in a single animal. The form may be well compared to the modern _Amphiuma_ so far as appearances are concerned; structurally they are widely separate. This species is one which is peculiarly characteristic of the Linton fauna. Measurements of Ptyonius pectinatus Cope. _Nos. 107 and 1094 G, American Museum._ mm. Length of specimen 137 Length of skull 26 Posterior width of skull 8 Interorbital width 3 Diameter of orbit 1.5 Vertical expanse of vertebra 6 Width of neural fan 2 Diameter of pedicel 1 _Measurements of a small jaw, No. 8555 G, American Museum._ mm. Length of jaw 15 Greatest width 1.5 Length of tooth 1 _Measurements of specimen No. 4438, U. S. National Museum._ mm. Length of specimen 65 Length of skull 22 Width of skull 6 =Ptyonius vinchellianus Cope.= Cope, Proc. Am. Phil. Soc., p. 177, 1871. Cope, Geol. Surv. Ohio, II, pt. II, p. 376, pl. xxviii, fig. 1, 1875. Type: Specimen in the American Museum of Natural History. Horizon and locality: Linton, Ohio, Coal Measures.