SAUROPTERYGIA. 169 



in the type-species, P. dolichodirus ; all the phalanges are elongated, 

 and the third and fourth are the longest digits. In the pelvic girdle 

 the pubes are relatively large, not pierced by any foramen ; the slender 

 ilium seems to articulate only with the ischium. The pelvic is almost 

 identical with the pectoral limb, though its phalangeal formula in P. doli- 

 chodirus is apparently increased to 4, 7, 10, 9, 7. The abdominal ribs 

 Itetween the pectoral and pelvic arches are especially robust, in three 

 paired and one median series, those of the latter not angularly bent or 

 keeled. The typical species is Plesiosaurus dolichodirus, attaining a length 

 of about three metres, from the Lower Lias of Lyme Regis ; P. macro- 

 cephalus and P. conybeari are larger species, known by tolerably complete 

 skeletons from the same locality, the latter sometimes more than five 

 metres in length. A fine large skeleton from the Upper Lias of Wlirtem- 

 berg, now in the Berlin Museum, is named P. guilelmi imperatoris. 



Cryptoclidus (figs. 102 c E, 106 E, 107). A genus much resembling 

 Plesiosaurus in the general proportions of the animal, but differing in having 

 all the ribs single-headed, and in the reduction of the clavicular arch con- 

 comitantly with the downward and inward extension of the scapulae which 

 meet in the middle line. The head is small and the mandibular symphysis 

 short. In the typical species about 32 cervical vertebrae can be counted, 

 and the cervical ribs are scarcely expanded distally. The trunk comprises 

 nearly 30 vertebrae, of which three or four may be regarded as sacral. The 

 clavicular arch (figs. 102 c E, cl.) is reduced to a pair of triangular 

 clavicles which meet in the middle line ; and in the adult the scapulae 

 grow together below in the median line, where they also become fused with 

 the forward process of the coracoids (fig. 102 E). The vestigial clavicles in 

 the adult are thus entirely on the visceral aspect of the inferior processes of 

 the scapulae ; immature specimens are known, on the other hand, in which 

 (fig. 102 c, fig. 107) the clavicular arch occupies its more normal position 

 as in Plesiosaurus (fig. 102 B). The pubis is relatively large, not pierced 

 by a foramen : the slender ilium articulates only with the ischium. Both 

 humerus and femur are much expanded distally, each articulating with 

 three bones, which seem to be radius, ulna (tibia, fibula) and an ulnar 

 (fibular) sesamoid. The abdominal ribs are proved to occur in three paired 

 and one median series. Fine skeletons, in all stages of growth, have been 

 obtained from the Oxford Clay of Peterborough. 



Pliosaurus. Imperfectly-known gigantic Plesiosaurs of Upper Ju- 

 rassic age, with relatively large head and short neck. The symphysis of 

 the mandible is considerably elongated. The cervical vertebrae are very 

 short, the cervical ribs double-headed, and all the vertebral arches loosely 

 articulated with the centra. Pliosaurus grandis occurs in the Kimmeridge 

 Clay, and P. ferox in the Oxford Clay. 



Cimoliosaurus and other genera represent Cryptoclidus 

 in the Cretaceous of Europe, N. and S. America, and New 



