20 



DR. R. BROOM ON THE 



temporal fossa, have so much superficial resemblance to the 

 Synapsid type that the larger majority of zoologists have 

 concluded that they are really allied to the Mammal-like reptiles. 

 These are the Plesiosaurs, In 1904 I first pointed out that the 



Text-fieiu-e 2. 



Illuitratioiis of temporal regions in a Plesiosanr, Placodonts, and a Clielonian. 



A. Skull o{ Plesiosmu'us macrocepliahis Owen. From skull in Brit. Mus. 



B. Skull of Placodus sp. From skull in Brit. Mus. 



C. SliuW oi Placochehjs placodonta Ji\eke\. After .Jaekel. 



D. Skull of Pelomedusa galeata. 



fossa in the Plesiosaurs is really formed between tlie parietal 

 above and the postorbital and squamosal below, and that it is 

 thus the homologuc of the upper fossa in Sphenoilon and not of 



