592 PROF. H. G. SEELEY ON THE 



The articulation with the vertebral column is not clearly shown, 

 because the atlas is in close apposition with the back of the head. 

 The teeth are few and imperfectly displayed ; they are long, slender, 

 and extend outwards at right angles to the jaw. 



The palate closed in the median line is common to Noihosaurus 

 and Pareiasaurus, and is seen in certain Amphibians, Chelonians, 

 Crocodiles, and other orders, so that it gives no clear indication 

 of affinities. Prof. Cope finds that the head of Stereosternum is 

 also elongated, with slender teeth ; but the details of the structure 

 have not been determined. 



The cervical vertebrae nre short, narrow, wider in front than 

 behind, in close contact, with a median ridge moderately elevated 

 on the base of the centrum. On each side of the ridge the base of 

 the centrum is concave, owing mainly to the development of a strong 

 tubercle at the anterior angle of the side of the centrum. These 

 tubercles are compressed from above downward, and each apparently 

 gave attachment to a rib by a facet which is less than half as long 

 as the centrum. Eight cervical vertebrae have a length of 3*25 

 centimetres. The first three are very short, the atlas shortest. It 

 appears to terminate in front in a concave articular cup. The other 

 centrums are rather less than | centimetre long. 



The cervical ribs have large heads, which articulate with the lateral 

 tubercles, but appear otherwise to be slender rods which lie near 

 to the sides of the vertebrae and are about 1 centimetre long, which 

 is unlike both the figure of the type of Mesosaurus, which has trans- 

 versely expanded cervical ribs according to Gervais,^ and the cast of 

 the specimen, though these maybe onlythe expanded heads of the ribs. 



In the lateral aspect the cervical vertebrae are concave from above 

 downward. The zygapophyses are well developed and strong ; they 

 lean a little forward. The foramen for the intervertebral nerve is 

 developed vertically, and chiefly excavated at the posterior borders 

 of the vertebrae. 



Beyond the eighth centrum the vertebrae have a different form. 

 The median ridge gives place to a convex base to the centrum, from 

 the sides of which strong transverse processes are given off. No 

 divisions can be seen between the centrums of the vertebrae 9-11, 

 and they look as though anchylosed. But, since they are curved, 

 that is impossible ; and I suggest that the aspect is a delusive 

 appearance which not improbably results from the presence of a 

 thin osseous film which extends over the sutures. The position is 

 that which would be occupied by the stalk of the interclavicle or 

 forward prolongation of the precoracoid. Extending transversely 

 outward from the suture between the eighth and ninth vertebrae 

 are fragments of a transversely extended median bone. On the left 

 side it extends outward and backward to the scapula, so that the 

 bone has the relations of the clavicular mass in Plesiosaurs. The 

 preservation is such that its nature cannot be determined with cer- 



^ The cast and the figure differ materially, especially in the structure of the 

 skull ; and I suppose the figure to be more accurate, since it corresponds better 

 with this fossil. - 



