600 



PROF. H. G. SEELET ON THE 



Pig. 3. — Early caudal vertebra 

 of Stereosternum. 



are somewliat similar to those in the Kimberley Mesosaurus, in 

 which they decrease in length very rapidly and are thicker, so as to 

 have a dissimilar aspect. Seventeen 

 caudal vertebrae are preserved. In 

 the first twelve the form is flat- 

 tened, and they differ only by de- 

 creasing in size. In the later 

 caudal vertebrae there may be a 

 large intercentral ossicle, almost as 

 large as the exposed part of the 

 centrum. The chevron bones are 

 attached to these ossifications. 



This suggests that chevron bones are the transverse processes or 

 caudal ribs of the intercentrum. The chevron bones are a little 

 longer than the centrum, and lie parallel to its base. 



The shoulder- girdle is imperfectly preserved. The coracoid in 



Natural size. 



Fig. 4. — Part of the slioulder-girdle of Stereosternum tumidum. 



Natural size. 



sc, scapula ; h, humerus. 



R. 537 is evidenced by an impression and some bone tissue, but its 

 form is not defined. In R. 536, Brit. Mus., there are indications of 

 a pair of wide, thin, crescentic bones in advance of the shoulder- 

 girdle. In extending above the humeral articulation they correspond 

 in position with the lateral plates of the Plesiosaurian scapula, and 

 are of not dissimilar form. I cannot regard them as scapulae because 

 they do not enter into the glenoid cavity. Prof. Cope only records a 



