and Clavicular Arch in Sauropterygia. 



141 



measures 3 inches from front to back, and the other an inch more. 

 Their internal borders are concave and sinuous, recalling the clavicles 

 of Plesiosaurus durobrivensis already described. It is probable that 

 the external processes of the clavicles now broken away were directed 

 outward and backward, and in form similar to that species. 



(ii.) A second Elasmosaurian clavicle, of different shape appa- 

 rently, is preserved in the skeleton No. 23, in which 77 vertebrae 

 were found. It has the vertebrae nearly flat at the articular ends, 

 with the transverse measurement and depth of the centrum similar. 

 Neither the neural arches nor cervical ribs are anchylosed, but both 

 have relatively deep attachments. 



In this species only one clavicle is preserved, but its form is per- 

 fect. One half of the other clavicle was found, but no trace of an 

 interclavicle, though I suppose both of these bones to have rested 

 upon the interclavicle, much as in the species just described. The 

 bone is triradiate, 4 inches long and as wide. Its inner margin is the 

 shortest, and is concave and slightly irregular. The superior and 



FiQ. 8. — Clavicle of Murcenosaurus (sp.). 



inferior processes are about twice as wide as the external process, 

 which is relatively long and slender. The anterior margin is concave. 

 What I suppose to be the posterior margin is also concave, but a 

 rounded prominence occurs on its inner third, and breaks the contour 

 into a long external curve and a small inner notch. 



The external termination is slightly widened and obliquely trun- 

 cated, as though for attachment. 



(iii.) A third form of clavicular arch, which appears to be prob- 

 ably of the same type, is represented by the imperfectly preserved 

 interclavicle in the skeleton No. 26 in the Leeds Collection (Brit. 

 Mus.). The scapulae in this specimen are badly preserved, but they 



