494 REPORT OF NATIONAL MUSEUM, 1898. 



duced anteriorly and is continuous with the small cartilaginous procora- 

 coid. Interclavicle posterior to the coracoid cartilages and overlapping 

 the anterior border of the sternum; its anterior axis very short, the 

 posterior still shorter. Sternum transverse, subcrescentic, cartilagi- 

 nous, not supporting any ribs. 



In the cervical vertebne the odontoid process is sliort, and is coos- 

 sified. There are six intercentra; the sixth low, the rest rather promi- 

 nent. All the cervicals have ribs, except the axis and third. No zygo- 

 spbene; prezysapopliysial faces not reflected on neural arch. Diapo- 

 physes very short; neural spines moderately elevated, especially on 

 cervical and caudal regions. On the latter they are rather narrow and 

 stand at the posterior border of the neural arch, looking backward. 

 At the anterior border is a second short spinous neural spine, which 

 looks forward. A gap, which is roofed by membrane, separates the 

 anterior from the i^osterior borders of the neural arches. The centrum 

 is not segmented, but breaks very readily immediately behind the cup 

 and in front of the diapophyses. Chevron bones coossified with the 

 middles of the centra, and not interceutral. The centra, except at the 

 ball-and-socket articulations, are quite as attenuated as the neural 

 arches, whence their great fragility. 



Pelcic arch. — Ilium short, proximally in contact with a single ver- 

 tebra, distaliy confluent with the rudimental pubis and ischium, which 

 form together an oval plate, entirely lateral in position. 



Posterior limb. — This is an undivided short rod of cartilage, which is 

 loosely articulated to the posterior concavity of the pelvic element, 

 thus marking the position of the acetabulum. All the teeth simple and 

 with acuminate apex. 



Besides the peculiarities resulting from the reduction of the extremi- 

 ties, this genus differs from Gerrhonotun as follows: The presence of 

 maxillopremaxillary foramen; the isolation of the anterior part of the 

 posterior narial fissure as a foramen; the coossification of tlie sphenoid 

 and basioccipital bones. The nonsegmentation of the caudal centra; 

 the presence of two neural spines on them, and the very peculiar 

 chevron bones. 



But one species of this genus is known. Boulenger unites the genera 

 Pseiidopus, Hyalosaurus, and Bopasia with it; but Pseudopus and Hya- 

 losaurus have posterior limbs, and I have shown that Dopasia has no 

 interclavicle.^ Hyalosaurus also has the auricular meatus closed. 



OPHISAURUS VENTRALIS Linnaeus. 



Ophisaurus ventralis Daudin, Hist. Kept., VII, p. 352, pi. i.xxxvni.— Oppel, 

 Ordn. Kept., 1811, p. 45.— CuviEU, Regue Anim., II, 1817, p. 59.— Fitzinger, 

 Neiie Cl,i8.s. Kept., 1826, p. 50.— Harlan, Jour. Acad. Nat. Sci. Phila., 1827, V, 

 p. 346.— Wagleii, Syst. Ajuph., 1830, p. 159.— Gray, Syu. Rept. Griff. Cuv., 

 IX, 1831, p. 65.— AViEGMANN, Herp. Mex., 1834, p. 11.— Dumeril and Bibkon, 

 Brp. G6n., V, 1839, p. 423.— Duveiwoy, Rfegne Anim. Rept., pi. xxiv, fig. 1.— 



1 Journal of Morphology, VII, 1892, p. 229. 



