Vih MARINE EEPTILES OF THE OXFOED CLAY. 



hand, considers that both fossae were developed, but that the lower temporal bar had 

 been lost. The present writer* also, chiefly on account of the structure of the palate, 

 once regarded the Sauropterygia as descended from a primitive Rhynchocephalian 

 reptile. Boulengerf considers, as SeeleyJ did, that Mesosaurus is closely 

 related to the Sauropterygia ; but the skull in Mesosaurus is too imperfectly known 

 to be certain of its relationships either to the Sauropterygia or any other order, 

 though it has been referred by Osborn § to the Diaptosauria, a group including the 

 primitive Bhynchosaurian types. 



A. S. Woodward and Williston, especially the last-named author, consider the group 

 as nearly related to the Theriodontia, a view which is here adopted, the arguments 

 against the relationship of the two groups having been to some extent weakened by 

 recent discoveries among the South African Therapsids. 



The primitive Sauropterygian may be regarded as probably possessing the following 

 characters : — 



Skull with a single temporal fossa, the zygomatic bar being formed by the squamosal 

 meeting the jugal or postorbital or both ; large pineal foramen ; fixed quadrate ; 

 palate with vomers (prevomers) separating the internal nares and meeting the anterior 

 ends of the pterygoids behind; a transpalatine and epipterygoid present; a well- 

 developed paiasphenoid (vomer) uniting posteriorly with the basisphenoid ; postfrontal 

 present and, in some cases, excluded from the temporal fossa ; prefrontal and lachrymal 

 present, at least in some, and a septo-maxillary (postnasal of Jaekel) occurring at least 

 in Simosaurus and Kotkosaurus. Teeth on the edge of jaws thecodont; small teeth 

 on pterygoids (in Lariosaurus). 



The shoulder-girdle with strongly devcToped clavicular arch ; probably a separate 

 cartilaginous precoracoid ; coracoid not greatly expanded, and scapula without largely 

 developed ventral ramus. The pubes and ischia not greatly expanded, and joining 

 the ilium in the acetabulum in a triradiate suture; there may be a pubic foramen 

 or notch. The limbs ambulatory, not modified to form paddles, there being no 



* "On the Structure of the Plesiosaurian Skull," Quart. Journ. Geo!. Soe. vol. Hi. (1S96) p. 246. 



t " On a Nothosaurian Eeptile from the Trias of Loinbardy, apparently referable to Lariosaurus," 

 Trans. Zool. Soc. vol. xiv. (1896) p. 1. 



t "The Mesosauria of S. Africa," Quart. Journ. Geol. Soc. vol. xlviii. (1392) p. 580. 



§ "The Reptilian Classes Diapsida and Svnapsida, aud the Early History of the Diaptosauria," ifern. 

 Amer. Mus. Nat. Hist. vol. i. (1903) p. 45L 



