Cope.] bJS [Jan. IS, 



while the width exceeds both. The basioccipital bone is prominently 

 keeled on the middle line, so that the section is a V of a more compressed 

 character than the section of the same in M. superbus. The median plane 

 of the sphenoid is prominent, and is continued as a wedge with the apex • 

 opposite the posterior borders of the otic bullae. The palatine borders are 

 parallel, except where they form on each side an open angle at the junc- 

 tion of the descending process of the sphenoid, which is here directed for r 

 wards. Its external border is distinct from that of the palatopterygoid 

 plate, and makes a groove with it. The maxillary bone is not produced 

 posterior to the notch on either side of the base of the posterior production 

 of the palatine bones. The middle line of the latter is deeply concave 

 opposite the former, and the palate is also especially concave between the 

 first true molars. The palate is flat between the first and second pre- 

 molars. The inferior surface of the squamosal process of the zygoma is 

 roughened for the origin of the masseter muscle. The inferior edge of the 

 malar comes from its inner side, and is narrow and with a median groove. 

 Its inferior edge is continued as a ridge of the maxillary as far as opposite, 

 the anterior lobe of the second true molar. The maxillary bones are more 

 produced anteriorly than in any of the other species. The apex of the 

 nasal bones stands above the posterior border of the canine in this species ; 

 above the anterior edge in M. superbus, M. clielydra and M. leidyi (fide 

 Bettany). The posterior border of the nares is above the anterior part of 

 the first premolar in the three species named, except M. chdy&ra where it 

 is over the posterior edge of the canine : in M. macrostegus it is above the 

 posterior edge of the longer first premolar. 



The infraorbital foramen is large, and its posterior border is above the 

 anterior root of the first true molar. The incisive foramina are large, and 

 each one is a little longer than wide. The nareal opening contracts gradu- 

 ally to its inferior apex. There is a considerable maxillary foramen op- 

 posite the middle of the fourth superior premolars. The posterior nareal 

 is not large ; its anterior outline is regularly concave. Its lateral (sphe- 

 noid) borders reach to opposite the anterior faces of the postglenoid pro- 

 cesses and bound the foramen ovale on the inner side. The latter is round, 

 is rather small, and is opposite the middle of the postglenoid surfaces. 

 The foramen rotundum on the other hand is large and vertically oval, 

 and is bounded below by a transverse prominence of the base of the ali- 

 sphenoid bone. It probably includes the sphenoorbital foramen, a foramen 

 anterior to its inferior border probably communicating with the nareal 

 chamber. The optic foramen is small, and is situated opposite the ante- 

 rior two-fifths of the zygomatic fossa and a little above the line of the 

 apex of the foramen ovale. The foramen lacerum is ovoid and not large. 

 The posterior foramen lacerum is a transverse sigmoid, one extremity 

 being the jugular foramen. The mastoid and postparietal foramina are 

 of moderate and equal sizes. No postsquamosal or supra- or postglenoid 

 foramina. 



The animal described is too old to exhibit sutures. 



