NO. 7 



EARLY CENOZOIC VERTEBRATES FRIES ET AL. 



II 



Exhibiting only moderate dorsoventral depression, the skull has a 

 quadrangular profile when viewed from the side. 



The braincase, because of the hardness of the matrix and conse- 

 quent danger of damage, has not been completely exposed. Observ- 

 able, therefore, are only the thoroughly co-ossified bones of the 

 occiput and the ventral cranial basis. The occipital region is badly 

 eroded but articulates loosely with the skull roof above and appears 

 to have had a depth two-thirds its width. The paroccipital processes 

 are indicated to have been short and to have projected outward and 

 slightly forward. When viewed from below, the fused basioccipital 

 and basisphenoid elements comprise a plate of quadrangular outline. 



pmx 



Fig. 4. — Paradipsosaurus mexicanus, new genus and species (U.S.N.M. 

 No. 20667). A somewhat restored diagram of the skull in lateral view. Ap- 

 proximately X 3- 



Abbreviations: c, coronoid; d, dentary; sa, surangular. (Other abbreviations 

 as in fig. 4.) 



A deep emargination on each side separates the anterior basipterygoid 

 processes from the posterior basioccipital processes. The margins of 

 the posterior portion of the plate are strongly produced and the sur- 

 face of the part is, thus, markedly concave in both sagittal and trans- 

 verse sections. 



The single fused parietal would appear to be approximately one- 

 third wider than it is long. Its dorsal surface is practically flat and 

 shows a faintly rugose texture. This latter surface is sharply de- 

 limited by cristae from both the ventrolateral and ventro-occipital 

 laminae. Emargination of the dorsal plate by the supratemporal 

 fossae laterally and by the dorsal body musculature posteriorly is 

 shallow. Posterolaterally the parietoquadrate arch appears to have 

 been well elevated, and the anterior parietofrontal suture is straight. 



