Varanosaiiras acutlrostris^ BroHi. 309 



14. The considerable resemblance between the humeri of 



the two types. 



15. The sudden thickening of the symphysis between the 



pubes. 



16. The femora present many curious resemblances. 



The types differ in the following features : — 



1. The snpraoccipital of Labidosaurus is narrow and quite 



unlike that of Varanosawus. 



2. The post-temporal fossae are not small and widely 



separated in the Captorhinidte. 



3. The angular is not flat and tl>e lower jaw not in the 



least Therapsid in Labidosaurus. 



It will lie noticed that those features in which the two 

 types differ are characteristic of the Therapsid group as a 

 whole. 



Of the other typical Therapsid characters, the most im- 

 portant are the high brain-cavity and the low position of the 

 ear, of which the material at my disposal did not give quite 

 satisfacti)ry information, but sugiicests that in these features 

 Labidosaurus agrees with the Therapsid type. 



This series of resemblances and differences are exactly 

 what one would expect if the Captorhinidse are the compara- 

 tively little modified descendants of the group of Cotylosaurs 

 from which the Therapsid phylum sprung ; in curious 

 characters, mostly of trivial nior|)hological importance, 

 Vuraiiosauriis resembles them exactly. In the important 

 features which proclaim it a typical member of the Therapsid 

 stock, it differs entirely from them, witli pi'obably one very 

 important exception — that the brain-cavity of both types is 

 similar, and different from that of other Cotylosaurs and 

 other reptiles. If this is so, and it will be remembered that 

 the evidence is very unsatisfactory, we have again a fine 

 illustration of the fact that the leading part of evolution 

 takes place in the brain, changes in which long precede those 

 of other parts of the organism. 



One interesting point on which light is shed by Varano- 

 saurns is tlie identification of the temporal bones. 



There is not the faintest doubt that the bone I have called 

 sqnamosal is the same as the mammalian bone of that name. 

 In all its relations aiid appearances it agrees with that of the 

 Deinoceplialia, from which we have a continuous series, with 



Anil. (I; M<i(j. S. llisl. Ser. .S. Vol. xiii. '21 



