270 G. T. BETTANT ON THE GENUS MERYCOCHCERTTS. 



and downwards; its surface is remarkably even, unmarked by 

 furrows or prominences. 



3. A plane lying on the orbit is directed more obliquely down- 

 ward and forward than the infraorbital arch. Thus the eye would 

 look considerably forwards and upwards as well as outwards. The 

 orbit is larger and more oval than in M. Leidyi. 



4. The very great outward extension of the zygomatic arch. 



5. The great size of the posterior zygomatic crest and of the tem- 

 poral fossa, whose long axis makes between 10° and 15° greater 

 angle with the middle line than in the following species. 



6. The greater breadth and size of the postglenoid process. 



Merycocekerus LEiDn, n. sp. PI. XVIII. 



I desire to connect this species with the name of Prof. Leidy, 

 whose magnificent works have done so much for our knowledge of 

 the paleontology of North America. 



It is founded on a large skull, which is nearly complete, lacking 

 unfortunately the posterior part of the zygoma with its crest on 

 both sides, and also the orbit and the suborbital arch on the left 

 side. The face, however, is almost perfect, the fore part of the 

 nasals only being injured. The mandible is firmly united by the 

 matrix to the skull almost in situ, but a little laterally displaced 

 behind. The front teeth are a good deal broken ; the lateral view 

 of the teeth of the upper jaw is very good, especially on the left 

 side ; the lower premolars are also partially visible. The occipital 

 crest is injured behind. The comparatively small portion of the 

 base of the skull that exists behind the glenoid articulation is well 

 exposed; but the auditory bullae and paroccipital processes are 

 almost entirely destroyed. The occipital condyles are very per- 

 fectly preserved. 



The characteristics of M. Leidyi are as follows, in contrast to 

 those of M. temporalis given above : — 



1. The lachrymal pits are conical at the bottom and of consider- 

 able depth ; there is a moderate-sized lachrymal tubercle on the 

 margin of the orbit. 



2. The infraorbital arch, of somewhat greater depth than that of 

 M. temporalis, is almost vertically situated. Instead of being flat, 

 it presents from above downwards : — first, the raised rim of the orbit ; 

 secondly, a broad groove passing round from the fore part of the 

 lachrymal depression and backwards on the lower fork of the malar, 

 being overhung by the strong prominence of the anterior part of 

 the zygomatic process itself where it fits into the malar ; and, 

 thirdly, the convexity of the malar process of the maxillary bone, 

 which gradually dies away forwards on the side of the face, and 

 becomes quickly lost behind. 



3. The orbit is considerably more vertically placed than in 

 M. temporalis, and looks much more directly outward ; it is nearly 

 circular. 



4. It is impossible to determine how far the zygomatic arches 

 extended outwards ; but from the direction of the parts existing, 



