PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



63 



The nasals are too incomplete to describe fully. They were narrow and seem 

 to closely resemble the same bones in Dimetrodon, indicating that, as in that genus, 

 the skull was narrow and high in the facial region. The cast of the top of a skull 

 observed in a large boulder in the field shows the same character. 



The mandible (fig. 39 a) of the right side is complete, with the exception of 

 the articular region. It resembles very closely the jaw of Dimetrodon. The only 

 difference noticeable is the sharp upward bend of the anterior end, causing the 

 anterior teeth to point backward at a considerable angle with the axis of the jaw. 

 This is, in part at least, due to distortion of the right mandible, since the ramus 



Fig. 38. Sphenacodon ferox Marsh, X ,'2. A, right maxillary, imperfect; B, inner surface of 



fragment of second right maxillary. 



of the left side does not show this character to anywhere near the same extent. 

 The sutures, so far as they can be made out, are identical with those of the Dime- 

 trodon mandible. 



The pterygoids are represented by the external processes only; they are indis- 

 tinguishable from the same processes in Dimetrodon. A single row of medium- 

 sized, conical teeth is found on the lower margin. 



The lower rim of the orbit, formed by the maxilla and jugal, the postorbital 

 bones of the two sides, and the quadrate are indistinguishable from the same 

 bones in Dimetrodon. 



Fig. 39. Sphenacodon ferox Marsh, X 



A, inner surface of a right ramus; B, quadrate. 



There can be no doubt of the great resemblance of the skull of Sphenacodon 

 and Dimetrodon so great a resemblance that, on the strength of this part only, 

 we would not be justified in considering the genera distinct. 



Three imperfect scapula are preserved in the collection. One, associated with 

 a considerable part of the skeleton in a bad state of preservation, is known only 

 from a fragment of the blade. Another, an isolated specimen, lacks the anterior 

 edge and has the two proximal bones attached (fig. 40 a). The third, also an iso- 

 lated specimen, lacks the anterior border and the border of the coracoids. As a 

 whole the shoulder blade is quite similar to that of Dimetrodon. The sutures between 



