Merriam.] 



A New Murine Reptile 



421 



forms. For the present the Thalattosauria may be placed in the 

 superorder Diaptosauria, though it is doubtful whether it will be 

 retained in that division <>r even whether the Diaptosauria can 

 hold together when the various forms included in it become 

 better known. With increased knowledge of the Triassic 

 reptiles, it will naturally become increasingly difficult to 

 determine whether or not some of the orders classed with the 

 Diaptosauria arc more deserving of a position in that group 

 than, for example, the rhynchocephaloid Parasuchia having an 

 independent position . 



Inside the Diaptosauria the closest affinities of the Thalatto- 

 sauria are with the Proganosauria and Choristodera. From 

 both groups they differ more widely than these two differ from 

 each other. In many respects, particularly in limb structure, 

 the Thalattosauria represent more highly specialized aquatic 

 forms than the other two orders. 



Outside of the Diaptosauria there are noticable resemblances 

 to the Parasuchia and to the Lacertilians. The common char- 

 acters are, however, almost without exception, primitive or 

 rhynchocephalian characters which we find persisting in the 

 Parasuchia and Squamata. 



♦ Some of the most interesting points of resemblance to known 

 forms shown by Thalattosaurus are found in its similarity in 

 parts of the skull to Proterosuchus Broom, from the Karoo 

 Beds. This form is referred to by Broom as "... a primi- 

 tive Rhynchocephalian which shows a considerable degree of 

 specialization along the line which gave rise to the early Croco- 

 diles and Dinosaurs." Here as in other groups compared, the 

 skull structure shows important differences. Judging from 

 these differences and from the occurrence of Proterosuchus, we 

 may expect that the limbs in that form will prove to have a 

 structure very different from that in TJialattosaurus, and will 

 tend rather toward the crocodilian type. While showing note- 

 worthy affinities, it would lie impossible to bring Proterosuchus 

 and Thalattosaurus nearer to each other than related orders of 

 the Diaptosauria could conic. 



