1884. J 521 [Cope. 



possess the widely different position ascribed to this genus by Leidy. Few 

 if any of the characters given by Mr. Bettany as those of the genus, can 

 be regarded as other than characters common to several of its species. 

 Perhaps the most important of these is the angle formed by the basifacial 

 with the basicranial axis, by which the face is presented as much forwards 

 as upwards. The species present considerable variety in form. The ge- 

 nus embraces the largest species of the family, such as M. maerostegus, M. 

 superbus, etc. The characters of the species are as follows : 



I. Foramen infraorbital e above middle of fourth superior premolar ; pos- 

 terior part of zygoma expanded ; palate moderately produced posteriorly. 

 Squamosal part of zygoma less expanded anteriorly and with 



rounded border ; head elongated ; premaxillary bone not 

 produced ; otic bulla larger, compressed, extending anterior 

 to postglenqid process ; size large M. superbus. 



Head shortened occipitally, so that a line drawn through post- 

 glenoid and paroccipital processes makes 90° with the 

 middle line ; malar bone openly grooved below orbit ; 

 angle of mandible obliquely truncate M. leidyi. 



Squamosal part of zygoma most expanded in front, and elevated 

 behind, so that the cranium is as wide as from the paroccipi- 

 tal process to the canine tooth ; its posterior angle rising to a 

 level with the sagittal crest ; its inferior edge spread out- 

 wards ; its superior edge truncated ; occiput not shortened ; 

 malar flat below orbit ; postglenoid process marking front 

 of bulla M. chelydra. 



II. Foramen infraorbitale above the first true molar. Palate greatly 

 produced posteriorly. 



Squamosal part of zygoma much expanded, and with truncate 

 edge ; malar bone robust, prominent ; skull, width equal 

 length from condyles to first premolar ; maxillary produced 

 anteriorly ; frontal plane, transverse diamond-shaped ; 

 bulla small, conical, posterior to anterior edge of postglenoid 

 process M. maerostegus. 



Squamosal part of zygoma little expanded upwards or lateral- 

 ly, edge rounded ; malar bone flat ; bulla large, extend- 

 ing in front of postglenoid process ; front longitudinally 

 diamond- shaped, decurved at orbit M. montanus. 



III. Foramen infraorbitale above anterior border of second 

 true molar. 



Zygoma originating above second molar ; large ; incisors 



small (fide Leidy) M. rusticus. 



Zygoma originating above third true molar ; larger ; incisors 



large (fide Leidy) M. proprius. 



Of the above seven species, four are represented in my collection, some 

 of them by a large amount of material. The latter are from the John 



