ORDER SAUROPTERYGIA. 



I08l 



pleurodoii), which thus occupies a somewhat similar position to the 

 one held by Polyptychodon in the preceding branch. This genus 

 is represented by several species of gigantic Reptiles ranging from 

 the Oxford to the Kimeridge Clay, but of which derived remains 

 are also found in the Lower Greensand of Potton, in Bedford- 

 shire. The skull and teeth (fig. 1003) are relatively very large; 

 the former having a somewhat shorter mandibular symphysis than 

 in Peloneustes. The teeth are carinated, and in the Kimeridgian 

 species the space between the two carinas is nearly flat, and 



Fig. T004. — Diagram of the ventral aspect of the pelvic girdle of a young Pliosaur. The upper 

 bones are the pubes, and the lower the ischia. In the adult the ischia become more elongated, 

 and their inner borders should have been placed more nearly parallel. (After Phillips.) 



devoid of ridges. The neck is very short, and all the cervical 

 vertebras (fig. 1005) are relatively large, with nearly flat terminal 

 faces to the very short centra, which in the anterior region have 

 two distinct and often very prominent costal facets. A peculiar 

 feature of all the vertebrae is, that the arches were only articu- 

 lated to the centra by cartilage, so that they are always found 

 detached. The pectoral girdle was of the general type of that 

 of Peloneustes, but it is not improbable that the interclavicle was 

 absent. The humerus was shorter than the femur, and the 

 adius and ulna in the Kimeridgian forms have become much 



