858 THE JOHN DAY FAUNA. 



The following table represents the characters of the species so far as I 

 can determine them at present: 



A. Thickened superciliary ridges wanting; front wide. 



Superciliary borders obtuse, not continued into temporal ridges; front flat, or 

 little concave; premolars narrow. 



Length of skull .046 E. planifrons. 



Length of skull .038 E. minor. 



Superciliary borders sharp, vertical, continued into two straight temporal augles, 

 which form a V. 



Premolars narrow; size of E. planifrons E. lambdoideus. 



AA. Thickened ridge on the suijerior side of each supercilium ; front narrower. 



Superciliary ridges soon discontinued ; size of E. planifrons E. cavifrons. 



AAA. Superciliary ridges much thickened, soon uniting, and closinf, the frontal 

 groove behind. Front narrowest. 

 Premolar widened at the base; size of E. planifrons E. crassiramis. 



Some differences in the form of the mastoid bone may be observed in 

 species of this genus. Thus it is flat behind, and bears a well-marked 

 "lateral occipital" angle in E. planifrons and E. lambdoideus, while in the 

 remaining species it is convex, and with the angle little apparent. In some 

 specimens the loss of the hammer-shaped squamosal dismemberment, which 

 I will call the posttympanic bone, gives a deceptive extension forwards to 

 the mastoid. 



Parts of more than a hundred individuals of Entophjchus are in my 

 collection. 



Entoptychus planifrons Cope. 



Paleontological Bulletin No. 30, p. 3, December 3, 1878. Proceedings Amer. Philos. Soc, 1878 (1879), p. 65. 



American Naturalist, 1883, p. 170, fig. 18. 



Plate LXIV; fig. 1. 



A nearly perfect skull, with a portion of a second, are the only speci- 

 mens that I can certainly refer to this species. They represent the largest 

 size found in the genus. 



The muzzle is long, and gently decurved anteroposteriorly, and slightly 

 convex transversely The length from the side of the orbit at its anterior 

 border to the extremity of the nasal bones is exactly equal to the length 

 from the same point to the inion at one side of the middle line. The front 

 in the more perfect skull is slightly concave, but is without lateral ridges ; 

 in the less perfect specimen it is more nearly flat. There is no trace of 



