1884. | °41 [Cope. 



cranial region, zygomata, and left maxillary bone, have been lost. The 

 measurements of No. 4 somewhat exceed those of the other specimens, 

 so that it is doubtful whether it really belongs here. 



The characters which distinguish this form from the M. leptorhynchus 

 are not numerous. In the first place the front and muzzle are relatively 

 wider. Secondly, the larmier is of a different form. Instead of being a 

 horizontal slit, it is subtriangular, with the base above, and the angle 

 below ; thirdly the canine teeth are more robust in both jaws. But the 

 position of the infraorbital foramen is slightly variable, and the width of 

 the front in one specimen is about as in the sub-species leptorhynchus. 

 The size of the canine is not invariable. I am therefore precluded from 

 regarding the M. leptorhynchus as more than a sub-species. 



As compared with the M. elegans, the strong convexity of the side of 

 the face distinguishes it. The convexity continues from the malar region 

 forwards above the infraorbital foramen, and nearly reaches the nareal 

 opening. Judging from Leidy's fig. 11, Plate XI, of the Extinct Mam- 

 malian fauna of Dakota and Nebraska, the premaxillary bone of the M. 

 elegans is flatter than in the M. arenarum. The infraorbital foramen has a 

 more anterior position in the latter than in the former. 



The size is always a little larger than in the type specimen of 31. lep- 

 torhynchus. 



Measurements. M. 



No. 1. 

 Length from occipital condyle to postglenoid process. . . .037 



" " "' " " postfrontal process 076 



" " " " " preorbital border 105 



Transverse diameter of orbit 030 



Depth of malar bone at middle of orbit, 019 



" zygomatic process at glenoid face (greatest) . . .019 



Width at middle of supraorbital border 062 



" malar bones 096 



" zygomatic process of squamosal 100 



of occipital condyles 034 



" occiput at middle 036 



Elevation of occiput including condyles 054 



Depth of skull at right angles to profile at glenoid face. .041 



" " " orbit (exclus. teeth) 051 



" of mandibular ramus at m. ii 030 



" P-m. iii 022 



Length of last five superior molars 064 



" " true molars 043 



Diameters P-m. iii ( anteroposterior 010 



t. transverse 010 



t,. m . . .(anteroposterior 013 



Diameters m. i I v 



I transverse 013 



