and Clavicular Arch in Sauropterygia. 147 



Fig. 14. — Clavicles of Cryptoclidus platymerus. art, median articular surface. 



On the visceral surfaces of the scapulae are shallow depressions 

 terminating; outward in a sharp angle such as might have received 

 the external processes of clavicles like those found with the Leeds 

 Collection specimen No. 36. These impressions are symmetrical and 

 seen in both scapulae, and so far they support the interpretation of 

 this clavicular arch now offered. ~No evidence of an interclavicle was 

 met with, and there is no evidence of its existence. 



If the clavicles are correctly identified, their mode of occurrence 

 may account for the circumstance that they have not been observed 

 in Colymbosaurus. And their sutural union as in a Chelonian 

 may be regarded as a generic character, separating this type from 

 Murcenosaurus. 



An important generic character is found in great vertical depth of the 

 radius and transverse elongation of the ulna. It has been stated that 

 the ulna in another specimen consists of two separate bones* (' Cat. 

 Foss. Rep. Brit. Mus.,' Part II, p. 206), but I have been unable 

 to detect evidence of a suture between them, and regard the 

 division as a fracture. Extreme as is the divergence in proportion, 

 these bones are better compared with those of Murcenosaurus 

 than any other type. The separation of the ulna from the olecranon 

 characterises the genus Colymbosaurus, and is seen in C. Manselli 

 (Hulke sp.), in which the bones are in close union, in C. megacleirus 

 apparently, and in C. Portlandicus (Owen sp.), in which the bones are 

 ovate, less perfectly ossified, and separate. This species, No. 31, 

 may be a precursor of Colymbosaurus, but there is no reason for 

 referring it to that genus, which has the humerus long and narrow. 

 The first row of the carpus appears to have originally comprised five 

 bones, as in the Mesosauria ; but the small inner and outer elements 

 are now blended with the carpals next them, reducing the number of 



J* The fragments, which had been mended, have been separated. 



