AVD AVES OF NORTH AMERICA. 17 ly on the median line. Limbs distinctly developed. Ribs long, well developed. Scales none. In more detail, we have an elongate lanceolate head with little or no sculpture of the external surface of the bones. The angles of the mandibles are much prolonged backwards as in Apateon and frogs, and the well developed ribs commence but a short distance behind. the head. The vertebra are slender, and furnished with well developed diapoph) ses. The neural spines of dorsal vertebra in O. remex are flattened and expanded in the line of the vertebral column, and weakly grooved to their superior margin. Their char-acter has not been observed in the other species. The neural and haemal spines of the caudal vertebra are prolonged, and remarkably sculptured by longitudinal grooves, which are most distinct towards their terminations. They are much flattened to support an oar-like tail. Anterior limbs have been seen in two species, and posterior in one other. Though they all probably possess two pairs of limbs, this point is not entirely established, leaving the homogeneity of this genus still somewhat uncertain. A pair of symmetrical bones whose impressions are seen posterior to the occipital bone appear to be the coracoid, and one of them is followed by a second element, which is .probably the humerus. A third piece follows, which is ulna, or radius; the second bone of the forearm is lost, but some impressions, which appear to be those of a digit, are visible. The skin has been occupied by a great number of closely packed, curved, spine-shaped scales. They have occupied the ventral integument, passing from the median line of the belly outwards and posteriorly, having acute tips which may or not have penetrated the skin on each side. No such tegumentary spines protected the dorsal legion. The three sculptured dermothoracic plates common to so many of this order, have not been seen in this genus. As compared with Sauropleura, this genus is more elongate and snake-like, and with much weaker limbs; these characters are not sufficient to distinguish it alone, but as no dilated neural spines nor similar abdominal armature are discoverable in the former, I prefer to keep them separate for the present. • OESTOCEPHALUS REMEX, Cope. Sauropleura remex, Cope. Proc. Ac. Nat. Sci., Philada., 1868, p. 217. Oestocephaius omphiuminus, Cope. I. c. p. 218. Additional specimens receii ed from Dr. Newberry enable me to combine the caudal vertebrae described as above under the genus Sauropleura, with the remainder of the skek AMER!. PHILOSO. SOC.-VOL. xiv. 5
