92 AMERICAN PERMIAN VERTEBRATES 



Certainly in the Pelycosauria, and perhaps all the Theromorpha, 

 the quadratojugal does not enter into the boundary of the lower 

 vacuity and the bone is often, perhaps usually, absent. The 

 distinction, then, must be made exclusively on the union of the 

 postorbital with the squamosal below for the upper vacuity, their 

 separation for the lower. But this distinction is a not very con- 

 spicuous one; in the plesiosaurs, for instance, the postorbital 

 unites with the squamosal only in a slight point of contact; separate 

 them an inch and the vacuity would become the lower one as in the 

 Theromorpha, since there is doubtless no quadratojugal in the 

 Sauropterygia. On the other hand, Eroom figures the squamosal 

 of Tapinocephalus as broadly meeting the postorbital {Geological 

 Magazine, VI, 543), even moire broadly than in the plesiosaurs, 

 and yet the opening is assumed to be the lower one ! I confess that 

 to me the distinction between the upper and lower vacuities seems 

 to be one without a difference; nor can I see any evidence, in the 

 temporal vacuities, of phyletic distinctions between the various 

 single-arched types. Perhaps I am dull, but I am inclined to 

 believe that all single-arched reptiles have arisen from a single 

 type. 



It has been assumed that the squamate temporal arch has arisen 

 from a double-arched form by the loss of the lower arcade and the 

 development of streptostyly. But I beUeve that we are now 

 convinced that the Squamata are of quite as primitive a descent 

 as is the rhynchocephalian type, as urged by Huene and myself. 

 In Varanosaurus we have, in addition to the many marked skeletal 

 resemblances, presumably homoplastic, the loss of the lower arcade. 

 While it is improbable that such a type originally gave origin to the 

 Squamata by the development of an upper vacuity and the evolu- 

 tion of streptostyly, yet it is an interesting fact that just such 

 changes are all that are necessary to convert Varanosaurus from a 

 theromorph into a squamate, aside from the rib attachments, so 

 far as we yet know. 



Vertebrae and ribs (Plates I, II, III). — The vertebral column, as 

 shown in the mounted skeleton, was found in perfect articulation 

 from the skull to the forty-seventh caudal vertebra. A few of the 

 spines of the anterior vertebrae protruding from the surface of the 



