REPTILIA : VARANOSAURUS ill 



of genetic relationships, or merely primitive or "old-fashioned 

 characters," I am not prepared to express a decided opinion, but 

 I believe that they are genetic. Of the possession of two temporal 

 vacuities by Stereosternum or Mesosaurus there is no evidence 

 furnished by the numerous skulls that have been studied, and I 

 am firmly of the belief that there is but one. In the elongate 

 rostrum with posterior nares we have an aquatic modification, 

 which of course means wide specialization and adaptation to differ- 

 ent conditions. In the vertebrae there is a distinct resemblance, 

 as also in the ribs, which have been described as single-headed 

 and attached to the centrum, but attached below a transverse pro- 

 cess. I feel sure that the mode of union is like that of Casea, 

 and that the ribs are really double-headed, and their massiveness 

 is paralleled by the somewhat similar condition in Casea. The 

 posterior ribs were probably more or less anchylosed to the verte- 

 brae, as in both Casea and Varanosaurus. In the pectoral girdle 

 there are but few real differences. McGregor thinks there is 

 no procoracoid, but I have little doubt but that the structure 

 here is quite as in the Pelycosauria; the genus resembles those 

 of the Theromorpha too closely to be otherwise. The scapula is 

 more expanded, but that is an aquatic adaptation. The front 

 extremity seems to be quite like that of Varanosaurus; the expanded 

 humeri, the entepicondylar foramen, the structure of the tarsus, 

 and probably that of the feet, save the absence of claws. So, 

 too, the pelvis and hind extremity are very like. The pelvis has 

 an interval between the pubes and ischia as in Varanosaurus, the 

 tarsus is almost identical, and the feet, save the claws, also. Upon 

 the whole, given a single temporal vacuity, as I am confident the 

 Proganosauria had, I see no reason why the genera should not be 

 located in the same order with Varanosaurus, but in a separate 

 suborder, because of their aquatic adaptations. In any event I 

 have not a bit of faith in their rhynchocephalian relationships. 



Family Caseidae 



Williston, Science, XXXIII, 631, 1911. 



Crawling phytophagous theromorphs with short, broad, de- 

 pressed head, large body, long tail, and short legs, from four to 



