G. T. BETTANY ON THE GENUS MERYCOCHOSRUS. 269 



an angle of 40° with the horizontal. The two halves of the man- 

 dible do not appear to have become anchylosed at any period. They 

 are separated at the symphysis by an eighth to a quarter of an inch 

 in our specimens ; and the opposed surfaces are very simply denticu- 

 lated. The posterior and inferior margins of the mandible are 

 rounded and thickened, but are less thick at the angle. The lower 

 margins of the horizontal rami very gradually approach each other, 

 and meet anteriorly by forming a small semicircular curve at the 

 symphysis. Nothing can be said about the coronoicl process or the 

 inner surfaces of the rami, because the space between them in our 

 M. Leichji is filled up by peculiarly hard matrix. 



Since the species of MenjcocJioems founded by Prof. Leidy are 

 chiefly based on their teeth with portions of jaws, and I am not able 

 to determine their identity or non-identity with those in the Wood- 

 wardian Museum, I think it better to describe the two principal 

 forms which I have determined as new species, especially as they 

 are distinguished on grounds independent of the teeth. 



Merycocekerus temporalis, n. sp. PI. XTII. 



This species is founded mainly upon two specimens, numbered 

 2 and 3 in the list given above. The first of these is of unique 

 interest. Anteriorly it is vertically truncated in the region of the 

 third premolar. The frontal surface and the lateral walls of the 

 skull are entire. On the right side the margins of the orbit are 

 much injured, and the infraorbital arch is almost entirely lost ; but 

 the great zygomatic crest behind this is complete. Unfortunately 

 the ridge leading from the posterior part of the zygoma to the trans- 

 verse occipital crest is broken off, as is almost all the sagittal crest. 

 On the left side the orbit with its infraorbital arch is almost perfect, 

 but the zygomatic crest is deficient. Posteriorly the lateral occipital 

 fossce are plain, but they lack the bounding projecting ridges ; the 

 condyles are broken off. On the under surface of the skull the sur- 

 faces of the basioccipital and basisphenoid are almost perfect ; the 

 auditory bulla, the glenoid surfaces, and the postglenoid processes 

 are in excellent preservation ; and the palate, so far as the anterior 

 truncation, is complete. The teeth, however, are broken off, not 

 simply worn down. 



The other specimen is more complete anteriorly, and includes 

 considerable portions of the canines and the nasals up to their ante- 

 rior terminations. The sides of the face are more or less damaged ; 

 but the orbits can be pretty well defined, and the suborbital arches 

 are entire, with a little piece of the zygoma on the right side. The 

 greater part of the frontal surface is present ; but nearly the whole 

 skull behind the posterior boundary of the orbits is broken off. 

 Below, the palate is in a very imperfect condition ; the outlines 

 of a number of teeth are seen broken off down to the level of 

 the palate. 



The chief characteristics of M. temporalis are the following : — 



1. The lachrymal pits are wide and shallow. 



2. The infraorbital arch is directed somewhat obliquely outwards 



v2 



