MUSEUM OF COMPARATIVE ZOOLOGY. 169 



Upper Teeth. 



M. 

 Antero-posterior diameter of mo]ar-premolar series (pm. .065, m. .160), .225 



Measurement of the canines, outside 130 



" " " inside 056 



Diameter of first molar, antero-posterior .047 ; trans 068 



" third molar, " .060 " 064 



« fourth premolar, " .025 " 045 



« canine, « .035 " 035 



Lower Jaw. 



Length of sj'mpliysis, 130 



Breadth of jaw opposite canines ' 075 



Diastema behind the canines 050 



Depth of jaw below first molar 096 



Antero-posterior diameter of molar-premolar series 210 



Measurement outside of the canines 060 



Transverse diameter of the canines 030 



Antero-posterior diameter of the canines 037 



RHINOCERID^. 



Aceratherium (Rhinoceros) occidentale, Leidy. This species is abun- 

 dantly represented in the collection by skulls, teeth, and portions of the skele- 

 ton. Little more than the skull has been described as yet, but it is now 

 possible to give a nearly complete account of the osteology of this species, as 

 will be done in the final paper. The American species of Aceratherium are 

 lighter, more slender, and retain more evidence of lophiodont ancestry than 

 the European species, or any of the recent forms. The scaphoid does not 

 cover the magnum so extensively as, and the lunar has a greater contact with 

 the magnum than, in any of the modern genera, nor does the lunar rest so 

 completely upon the unciform as in the latter. The metacarpals are heavier 

 than in Hyrachyus, more slender than in the recent types ; there were plainly 

 four digits in the manus. The phalanges have about the same proportions as 

 in the Sumatran rhinoceros. In the hind foot, compared with that of living 

 species, we find that the tarsus is higher and narrower, the astragalus more 

 deeply grooved, with longer neck and smaller cuboidal facet ; the calcaneum is 

 not so heavy ; the metatarsals, especially the lateral ones, more slender. 



In the limb bones the processes for muscular attachment, such as the deltoid 

 hook of the humerus and third trochanter of the femur, are much less mas- 

 sively developed than in recent species. 



HYRACODONTID^. 



Hyracodon nebrascense, Leidy. This species is very abundantly repre- 

 sented. Its osteology has already been partially described in another place,* 



• E. M. Bull., No. 3, p. 17. 



