OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 403 



of snakes. The hind legs of Protorosaurus are longer than the 

 front ones, and this is the case also with Araeoscelis, though not 

 to the same extent. One can say with assurance that Araeoscelis 

 was an extremely light and slender, terrestrial and arboreal reptile, 

 with springing powers, and possibly with a parachute development 

 of the body membrane. Its length, when adult, was about 2 feet. 



THE SKULL OF CASE A' 



A preliminary description of the skull of Casea, as based on a 

 single, not quite complete, specimen, has been given by me in 

 my American Permian Vertebrates, with a promise of a further 

 discussion whenever the additional material of the University 

 collections should be worked out. One other skull has, so far, 

 been discovered and prepared, though there is still a probability 

 of others turning up in the future. This skull, unfortunately, 

 had been somewhat injured in the collection of the material by 

 the loss of much of the upper part in front of the parietal foramen. 

 The right orbit is nearly complete and the lower part of the left, 

 as also the lower part of the nares. The quadrates are somewhat 

 displaced, but otherwise the skull is more perfect than the one 

 previously described. The specimen is a part of a nearly complete 

 skeleton which has not yet been worked out of its nodular matrix; 

 it is of precisely the same size as the skeleton previously described. 

 The premaxillae are complete, or nearly complete, and are in posi- 

 tion with respect to each other and the maxillae. They project 

 farther forward than did the incomplete ones of the previous speci- 

 men, terminating above in slender processes, which separate the 

 nares narrowly. In the first-described specimen the nares had 

 been somewhat injured, with the roof depressed, especially on the 

 right side. The present specimen gives the lower side complete 

 and quite undistorted, enabling me to restore the orifice with the 

 aid of the other specimen, accurately, I think. It is possible that 

 the orifice may have been a little higher than I have figured it 

 (Figs. 9, 10). The nares, it is seen, are of enormous size, communi- 

 cating immediately with the very large internal openings below 



^ Williston, Jot(r. GeoL, XVIII (1910); American Permian Vertebrates (191 1). 



