704 PROF. OWEN ON THE RANK AND AFFINITIES IN 



five to seven in Iyuaaa and Amblyrhynchus (fig. 19) ; there is but one 

 in the Python (fig. 21). 



The argument which Prof. Cope derives from a study of the 

 mandibular fossils of his Mosasaurians runs as follows : — 



" Swallowing their prey entire, like snakes, they were without 

 that wonderful expansibility of throat due in the latter to an 

 arrangement of levers supporting the lower jaw. Instead of this, 

 each half of that jaw was articulated or jointed at a point nearly 

 midway between the ear and the chin. This was of the ball-and- 

 socket type, and enabled the jaw to make an angle outward, and 

 thus widen by much the space inclosed between it and its fellow "*. 



My first impression in reading the above was that the right and 

 left rami were meant by " each half of that jaw," and that the 

 " ball-and-socket " joint related to the form of the tympano- 

 mandibular articulation which differentiates the Mosasaurus from 

 both existing Lizards and from Serpents. But at p. 122 Prof. 

 Cope illustrates his meaning by a diagrammatic cut (fig. 4) which 

 " shows the appearance of the normal flexure of the ramus," at the 

 part, viz., which is marked s s in figures 18, 19, and 20, of the 

 present communication. 



§ 8. Vertebrae. — In testing the affinities of the Mosasauridce 

 by the characters of the vertebrae, I premise a brief notice of such in 

 the largest of the existing Lizards which have marine habits, viz. the 

 Amblyrhynchus crista tus t of the Chatham and Charles's Islands of 

 the Galapagos group, in one of which the abundance of these 

 lizards has given to an inlet which they frequent the name of 

 " Iguana Cove." 



The following are dimensions of the skeleton of an individual of 

 the species under review : — 



Amblyrhynchus (Oreocephaltjs, Gray) cristatus, Bell. 



ft. in. 1. 



Length of entire skeleton 4 4 



„ skull 3 5 



,, trunk (from occiput to sacrum) .... 1 3 6 



„ sacrum 1 



tail 2 8 



Number of vertebras 79, viz. : — 



of the neck 4 J 



of the dorso-lumbar region . . 20 



of the sacrum 2 



of the tail 53 



* Tom. cit. p. 45. 



t Bell in 'Zoology of the Beagle,' Keptiles, 23; also in ' Zool. Journal, 

 vol. ii. p. 204, pi. 12. This species is called " Oreocephalus cristatus " by 

 Gray, in his ' Catal. of Lizards,' l2mo, 1845, pp. xviii, xxv, & 189. Its osteo- 

 logy is well figured by Steindachner, ' Die Sclilangen und Eidechsen der 

 Galapagos-Inseln,' p. 303, taf. iii.-vii., and in ' Zeitschrift zur Feier des funf- 

 undzwanzigjahrigen Bestehens der k.-k. zoologiseh-botanischen Gesellschaft in 

 Wien,' 4to, 1876. 



\ Those, viz., without free pleurnpophyses. 



