Geological Paper's. 125 



lating with the parietal, jugal, postorbital and prosquamosal. The 

 prosquamosal (PSQ), on the other hand, is a very large bone, 

 articulating with the epiotic, parietal, squamosal and jugal above, 

 the quadrate and the quadratojugal below; and these seem to be 

 the relations of the other Permian air-breathers. 



The quadratojugal, or "postquadrate bone," as Cope has some- 

 times called it, is in reality not at all postquadrate. It unites in 

 front with the jugal above, behind with the prosquamosal and ap- 

 parently with the proximal end of the quadrate. In most speci- 

 mens by pressure it is turned inward so that its chief face lies 

 horizontal ; in life, however, it was evidently directed more down- 

 ward, forming by its frontal free border the margin of the fossa 

 into which the coronoid process of the mandible fitted. A view of 

 the left side of the specimen under discussion is shown in figure 3, 

 but I cannot be sure that the fossa and foramen are natural. On 

 the opposite side the fossa is less evident. In figure 3 I give a 

 cross-section of the side opposite to the one shown at a place cor- 

 responding to the arrow mark. There is a striking diflFerence in 

 the relations of the bone posteriorly in this specimen from those 

 seen in another remarkably good specimen, which must be deter- 

 mined as of D. magnicornis, in the deep notch between the pro- 

 tuberant end of the quadratojugal and the prosquamosal above, the 

 so-called epiotic notch of the earlier microsaurs. It was this 

 character which Cope laid stress upon as distinguishing his species, 

 D. limbatus. That the distal termination of the horn in this 

 specimen is a specific character seems hardly to be doubted. For 

 the present, therefore, I call the present specimen D. limbatus, 

 though the concavity of the posterior margin of the skull is quite 

 like that of specimens referred to D. magnicornis. 



The structure of the palatal region in this specimen has been 

 made out quite satisfactorily, save that most of the distinguishing 

 sutures are uncertain. The shape and arrangement of the parts 

 agree well in general with the figures given by Cope and Broili, 

 and there is not much to add to their descriptions. The transverse 

 bones are clearly separated by suture from the maxilla and pala- 

 tines. The quadrate seems to be free from the quadratojugals save 

 at the proximal end ; it passes upward and backward, to be at- 

 tached on the under side of the posterior part of the prosquamosal. 

 The exoccipitals pass outward a little in advance of the condyles 

 as a long, narrow process on each side, doubtless the confluent 

 opisthotic as far as the epiotics, uniting, for the most part, with 

 the parietals. Between these processes and the parietals and su- 



