ORDER SAUROPTERYGIA. 



IO69 



tation be correct, it will have the same homology in Nothosanrus?- 

 As specialisation proceeds it appears that the scapulae have tended 

 to develop very large ventral plates, with a concomitant reduction 

 and ultimate disappearance of the clavicular arch. The inter- 

 mediate stage is shown in Plesiosaurus (fig. 997), where it will 

 be seen that the ventral plates of the scapulae are separated in 

 the median line ; and the culmination in Cimoliosaiirus, where they 

 unite in a median symphysis, and join the anterior extremities of 

 the coracoids, while the 

 interclavicle has disap- 

 peared. Mr Hulke regards 

 the ventral plate of the 

 scapula as representing the 

 precoracoid of the Chelo- 

 nia, but further evidence 

 is required to prove this ; 

 the view that it represents 

 the clavicle being obviously 

 incorrect. In the pelvis 

 the pubis usually forms a 

 wide plate, while the isch- 

 ium is somewhat chopper- 

 shaped ; in some cases the 

 pubis and ischium of each 

 side unite to enclose an 

 obturator foramen. The 

 ischia are strikingly like 

 those of the Amphibia, and 

 have a long symphysis. 

 The limbs are subject to 

 considerable variation; 



those of the earlier generalised forms being adapted for progres- 

 sion on land, while in the specialised types they are modified 

 into paddles. In all cases, however, the limbs are readily distin- 

 guished from those of the Ichthyopterygia by the relatively longer 

 humerus and femur, and the absence of interdigital bones. The 

 limb-bones are regarded by Professor Seeley as showing signs of 

 Amphibian affinity. A peculiar feature in the limb-bones is that 

 the epiphyses (fig. 989) of the humerus and femur are enormously 

 developed, and form large cones at either extremity of the bones, 

 almost, or completely, meeting in the middle of the shaft, which 

 is reduced to a pair of elongated cups. The bones of the palate 



1 In the British Museum Catalogue of Fossil Reptilia Mr Hulke's interpreta- 

 tion of the homology of these bones was provisionally adopted, but the writer 

 now considers that the other interpretation is probably the true one. 



Fig. 988. — Ventral aspect ot the pectoral girdle of 

 Cimoliosaurus (cf) trochanterius ; from the Kimeridge 

 Clay. Reduced, sc, Scapula ; J>c, Ventral (precora- 

 coidal) plate of do. ; gl, Glenoid cavity ; f, Scapular 

 foramen ; co, Coracoid. (After Hulke.) 



