Skull of Mochlorhiuus platyceps. 



169 



which define the hinder border o£ the orbits. The bones are 

 better preserved on the left than on the right side, but 

 compression has partially closed the left orbit. 



The flattened upper surface of the head is smooth, slightly 

 concave from side to side, less than 4 inches long, and limited 

 behind by a transverse ridge. That ridge is made by the 

 interparietal bone, which is not vertical, but somewhat inclined 

 forward. The interparietal makes the upper part of the 

 occipital plate, and it abuts laterally against the pair of 

 parietal bones. The transverse ridge which divides them is 

 a slightly sinuous line of suture. 



parietal. 



temporal vacuity, 

 pjstfrontal. 



preparietal. 



prefrontal. 



nasal 



Superior surface of the skull of Mochlorhinus platyceps. \ nat. 



The lateral borders of each side of the roof of the head 

 include three areas : — First, the larger anterior part, which 

 lies between the prominent prefrontal and the postfrontal 

 bone, is the thickened, rounded, upper margin of the orbit, 

 which is concave from front to back, formed in the middle by 

 the frontal bone. Secondly, behind the orbits are the broken 

 bases of the external processes of the postfrontal bones, which 

 are thin, and probably descended in the usual way. Thirdly, 

 behind these missing postfrontal processes are the obliquely 

 inclined upper borders of the temporal vacuities. They are 

 concave from front to back, slightly convex from above down- 

 wards, over an inch long, and about j^ inch deep, margined 

 superiorly by a sharp ridge, which is a suture separating the 



