SYSTEMATIC REVISION OF THE SUBORDER. 23 



the external for a considerable distance as an acuminate laminiform process, in the 

 usual position of the quadrato-jugal bone. The production of the internal edge is 

 shorter, and its extremity is vertically truncate. Its superior edge fits an incurv-ature 

 of the superior edge of the pterygoid bone, and its internal face is applied to the 

 external face of the latter. 



" The pterygoid bone displays the sub triangular plate with dentigerous edges, 

 such as I have already described as present in the species of Dimetrodon. In this 

 species it is thinner and less massive than in any species of that genus yet known. 

 This specimen enables me to locate it more precisely than heretofore. The ptery- 

 goids were probably placed much as I have represented them to be, in the Empedias 

 molaris Cope (Proc. Am. Phil. Soc, vol. xix, p. 56, plate v). They send inwards a 

 subtriangular plate from each side, which approach each other on the median line 

 without touching, and the adjacent edges are somewhat decurved. The posterior 

 edges are deeply concave on each side of the middle line, and, like the inferior edges, 

 are dentigerous. The process for the quadrate extends outwards and backwards, and 

 is thickened on its posterior edge, while its anterior edge which is continued from 

 the inferior edge of the posterior border, becomes very thin. The anterior production 

 for the ectopterygoids extends outwards and forwards, leaving the anterior edge of the 

 dentigerous plates as the concave posterior border of the large palatine foramina. 

 The anterior production of the internal edge of the plate becomes very thin, and is 

 broken in the specimen without showing the articulation for the palatine. 



" The squamosal extends both above and below its anteriorly directed zygomatic 

 portion. The superior extremity shows squamosal suture for the parietal. * * * 



" The premaxillary bones are distinct. The teeth of that bone and of the maxil- 

 lary are of unequal sizes. 



"The axis has an expanded neural spine, and a diapophysis for rib articulation, 

 but no parapophysis or capitular fossa. The two latter features characterize all the 

 vertebrje which follow as far as the lumbar series. 



"The column in the typical specimen is tolerably complete, with a break of 

 uncertain but probably not great length in '^front of the sacrum, and the loss of the 

 distal part of the caudal series. lutercentra of rather small size are present through- 

 out the series anterior to the sacrum. * * * The bases of the neural spines are 

 compressed; they were probably not elongate as in Dimetrodon, though they are 

 unfortunately broken off, except that of the third cervico-dorsal vertebra. Here the 

 spine is short and truncate above and rather wide antero-posteriorly. As in Ditne- 

 trodon there is no distinction between cervical and dorsal vertebrae. 



"The pelvis is well preserved and has the characters already assigned to 

 C. natalis Cope. The ilium has a process or narrowed continuation with parallel 

 sides, directed backwards and upwards, and bearing a keel on the middle line on the 

 internal side. The ischia are much produced posteriorly, and are separated by a 

 notch on the middle line posteriorly. 



"The head of the femur is expanded, including probably the homologue of the 

 great trochanter of the mammalia, and its articular face is crescentic, with obtuse 

 horns. There is a trochanter below it on the posterior edge of the shaft. The 

 condyles are inferior, and are separated by a deep groove above and a shallow one 

 below. The articular faces of the two condyles are continuous, forming an 00-shaped 

 figure. The proximal extremity of the tibia is wider than the distal, and the articular 

 face is uninterrupted. That of the distal extremity is a transverse oval." 



