and Clavicular Arch in Sauropterygia. 



145 



scapular bones. But in this species it has become small, is much 

 longer than wide, and placed between the scapulae in a way which 

 shows that it might by further decrease entirely disappear, or when 

 ossification obliterates the median suture it may become embedded 

 between the lateral ossifications of the precoracoid region, and cease 

 to be recognisable. But the clavicles might still persist on the 

 visceral surface of the scapulas if such a change took place. 



I refer all these types in which clavicles and interclavicle are 

 developed, and connected in the way described, to the genus Murceno- 

 saurus, of which the type has been already described.* In all these 

 species the ulna and radius, and tibia and fibula, are approximately 

 equal and sub-quadrate bones, usually with the radius and tibia 

 slightly the larger, meeting each other in both limbs, and enclosing 

 a foramen between what were in Plesiosaurus the long concave sides 

 of the bones. In the species last described there is an interesting 

 tendency, though a slight one, to vertical elongation of the radius 

 and transverse elongation of the ulna, both bones being about 

 2 inches wide, while the radius is inches long and the ulna 

 1 J inch long. The humerus in this type is 7 inches long and 4 inches 

 wide, with well-ossified facets for the radius and ulna, which are 

 mutually inclined, and meet at a sharp angle. 



Fig. 12. — Eadius and ulna of the same specimen. Ra., radius ; ZJT., ulna ; prox., 

 proximal margin ; dis., distal border. 



(v.) The specimen in the Leeds Collection (Brit. Mus.) numbered 

 31 has been referred to Cimoliosaurus eumerus (Phillips species), 

 (' Cat. Foss. Kept, and Amph., Brit. Mus.,' Part II, p. 205) ; but the 

 different forms and proportions of all the limb bones justify its separa- 

 tion, and as a sub-genus of Murcenosaurus it is named Gryptoclidus 

 platymerus. As compared with Murcenosaurus Leedsii (No. 25, Leeds 

 Coll., Brit. Mus.), it has the centrum broader, shorter, and more 



* ' G-eol. Soc. Quart. Journ.,' 1874, p. 197. At that time the shoulder girdle was 

 only known from fragments; and the account now given of the scapulae corrects 

 the conjectural restoration which was based on that imperfect evidence. 



