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DR. R. BROOM ON THE 



tlie top of the quadrate readily suggests that the posterior 

 squamoso-parietal arch has been pushed out, as it were, by the 

 unusual develoi">ment of the temporal muscle. And this is 

 conlirmed by the fact that occasionally, as in Hydromedusa, the 

 posterior arch is still met with. 



If we are right in this conclusion, we can hardly resist the 

 further possibility that the Chelonian is quite a near ally of the 



Text-fie'ure 3. 



A. Skull of ULvosaurus atavns Qucnst. After v. Huene. ^ iiat. size. 



B. akuW o( lohtli^osanri'.s cummuuis Cony]). After the reconstruction by 



Sollas, and with the missing squamosal added. 



Placodont. Jaekel has shown that Placochelys has a turtle-like 

 carapace. Perhaps it may yet turn out that Ohelonians are 

 extremely degenerate cousins of tlie Placodonts. 



Another group of aquatic reptiles that have caused some 

 trouble are the Ichthyosaurs. By some they have been held to 

 be aquatic specialisations from ;x Siihenodon-XikQ ancestor. Others 



