ORDER SQUAMATA. 



I H3 



vertebrae in the neck, and well-developed limbs. The vertebrae 

 have zygosphenal articulations. Actedsaurus, from the Cretaceous 

 of Austria, is an allied form. 



Suborder 4. Pythonomorpha. — The Mosasauroids are car- 

 nivorous marine Reptiles, frequently of large dimensions, and 

 ranging in time from the Upper Greensand to the topmost Creta- 

 ceous, with a cosmopolitan distribution. The body is much elon- 

 gated. The skull (fig. 1047) presents a strong resemblance to that 

 of the Varanidce among the Lacertilia, and has the nasals and pre- 

 maxillae welded together, the quadrates 

 very loosely articulated, teeth on the 

 pterygoids as well as in the jaws, and 

 frequently ossifications in the sclerotic 

 of the eye. The teeth are large and 

 sharp, and anchylosed by expanded 

 bases to the summits of the jaws. 

 There may be zygosphenal articulations 

 to the vertebrae, and the cervical region 

 may include more than nine vertebrae. 

 The clavicles are always, and the inter- 

 clavicle and sacrum generally, wanting ; 

 but Professor Marsh figures a sternum 

 in one genus. The limbs are modified 

 into paddles (fig. 1046), with no claws to 

 the terminal phalangeals, and no fora- 

 men to the humerus. The development 

 of the pelvis is, moreover, but imperfect, 

 and at least the majority of forms appear 

 to have been devoid of dermal scutes, 

 although Professor Marsh has recorded 

 their presence in one genus. 



Family Plioplatycarpid^e. — The 

 least specialised form seems to be the 

 genus Plioplaty carpus, of the Upper Cre- 

 taceous of Holland, in which both an interclavicle and a sacrum 

 are present ; on which account its describer, M. Dollo, regards it 

 as the type of a distinct family. 



Family Mosasaurid^e. — The whole of the remaining genera of 

 the suborder may be included in this family. One of the well- 

 known genera is Clidastes (from which Edestosanrus is regarded 

 by Professor Cope as inseparable), from the Cretaceous of North 

 America. This genus comprises numerous species, characterised 

 by the extreme elongation of the body, and their small or medium 

 size. In the skull the teeth, as in the next genus (fig. 1047) are 

 continued to the extremity of the premaxillae ; the vertebrae are 



vol. 11. R 



Fig. 1046. — Right pectoral limb 

 of Platycarpus ; from the Creta- 

 ceous of North America. One- 

 twelfth natural size. «, Scapula; 

 b, Coracoid ; c, Humerus ; d, Ra- 

 dius ; e, Ulna. (After Marsh.) 



