REPTILIA: VARANOSAURUS 105 



surface is slightly concave, with the posterior upper thickened 

 margin curved outward. The two bones meet in an acute angle, 

 forming a deep, narrow floor to the pelvic cavity. Between the 

 pubes and ischia there is a rather large diamond-shaped opening; 

 and this opening was doubtless pervious in life, that is, it could not 

 have been filled up by cartilage, I think, a distinct premonition of the 

 pubo-ischiadic vacuity of the Chelonia, if not of all modern reptiles. 



The peculiar structure of the pubes in this genus allies it with 

 the true pelycosaurs much more closely than with the Caseidae. 

 In life the animal rested in repose wholly upon the ischia, while 

 in the Cotylosauria the support of the body was equally distributed, 

 in some at least, upon both the pubes and the ischia, in both of which 

 the symphysis was far more massive than in the Pelycosauria. 

 Just what is the significance of the much elongated, expanded, and 

 platelike pubes I do not understand. 



The femur (Plate XII, Figs. 1-5) is moderately expanded at 

 either extremity, rather slender in the middle. The proximal 

 end shows a flattened surface, broader on its inner side, and curved 

 backward and narrowed at the outer side. The trochanter, on 

 the tibial side, is prominent, continuing backward the inner sur- 

 face of the bone; it has a small oval facet at its extremity, directed 

 proximad and ventrad. Between this projection and the outer 

 and proximal sides there is a broad, shallow, digital fossa, which 

 extends downward for a distance of about two-fifths of the length 

 of the bone. The trochanteric elevation is continued for a short 

 distance as a distinct adductor ridge. The shaft at the middle 

 is nearly circular in cross-section, and the bone is not much curved. 

 The inner border of the bone is deeply concave throughout; the 

 outer one much less so. The distal articular surface looks, for the 

 most part, inward at an angle of about twenty degrees, and back- 

 ward at about forty-five. Of the articular surface that part on the 

 outer side for the fibula is the broader, as in Dimetrodon, with a 

 considerable antero-posterior extent, its outer margin concave in 

 outline. The tibial articular surface is large, subtriangular in shape, 

 and fully as wide as the fibular surface antero-posteriorly. The 

 intercondylar groove in front is deep, that behind is shallow; the 

 width of the articulating surface connecting the fibular with the 



