342 W. R. Smellie — A New Oxford Clay Plesiosaur. 



form of the vertebrae, having twenty-nine cervicals, three pectorals, 

 and twenty-three dorsals, while Cryptocleidus has thirty-two cervicals, 

 three pectorals, and twenty-one dorsals. While the ossification is 

 more complete than that found in larger and more massive specimens 

 of Cryptocleidus, the posterior cervical ribs have remained free, 

 a condition which may have evolved to mitigate the excessive rigidity 

 which, as insisted on by Professor Williston, 1 must have existed in 

 the thick part of the neck. The measurements given below and 

 compared with Cryptocleidus will indicate some of the differences 

 existing in the shoulder-girdle and pelvis. The humerus is like that 



Proximal portion of left fore-paddle (outer side). (Type-specimen, V. 1091.) 

 About ^ nat. size, a, accessory ossicle (missing in original) ; h, head of 

 humerus ; hum. humerus ; int. intermedium ; in.c. V. fifth meta- 

 carpal ; m.r. ridges for muscle insertion ; p, pisiform (anchylosed to 

 ulna) ; r, radius ; rad. radiale ; tu. tuberosity of humerus ; %b, ulna ; 

 uln. ulnare. 



of Cryptocleidus in size and width of distal expansion, but the facets 

 on the distal end are necessarily different to permit articulation with 

 four elements in place of the two in Cryptocleidus. The epipodial 

 bones are veiy similar to those of Tricleidus in shape as well as in 

 number, and a well-marked foramen occurs between the radius and 

 ulna. The hexagonal pisiform is anchylosed to the ulna, whereas it 

 is free in Tricleidus. In some ways the specimen shows a curious 

 blending of the characters of Tricleidus and Cryptocleidus, the paddle 

 figured being a case in point, but in others it gives indications of 

 being a more highly specialized type than either of those genera. 

 The development of the shoulder- girdle has proceeded exactly on 

 lines laid down by Dr. Andrews, 2 imparting increased rigidity to 



1 S. W. Williston, Water Reptiles of the Past and Present, 1914, pp. 80 

 and 91. 



2 C. W. Andrews, Ann. Mag. Nat. Hist. (6), vol. xv, p. 345, 1895. 



