THE AMERICAN XA TURALIS 1\ [Vol. XXXVIIl. 



Broom has contributed a large nu 

 structure and arrangement of the 

 South African reptiles, which for the 

 first time throw a perfectly clear 

 light on their relationships to each 

 other. 



3. Order Placodonti.\. 

 {TncertcE sedis.) 

 The position of this order as typi- 

 fied by the genus Placodus, is still 

 very doubtful. It is characterized by 

 very large teeth in the palate, and by 

 the absence of teeth on the maxil- 

 laries and premaxillaries. It includes 

 littoral, shell-eating forms, which may 

 be an independent offshoot of the 

 Anomodontia, or may be more nearly 

 related to the Sauropterygia. 



Owen. 



The theory of the relationship of 

 the plesiosaurs to the Synapsida 

 and especially to the Anomodontia 

 and Testudinata still requires con- 

 firmation. The skull structure is 

 typically synapsidan. The shoul- 

 der girdle structure, so far as 

 known, in the Triassic plesiosaurs 

 is certainly more synapsidan 

 than diapsidan. Numerous resem- 

 blances to the Testudinata have 

 been pointed out. On the other 

 hand, certain of the oldest Triassic 

 plesiosaurs, such as Lariosaurus, 

 (Fig. I) closely approach the Diap- 

 sida in the phalangeal formula. 



