Cope.] 540 [Jan. 18, 



Measurements of Skull. M. 



Depth, of malar bone at middle of orbit 0195 



" " zygomatic process at glenoid face (greatest). . .021 



Width of top of muzzle at larmier 0175 



" at middle of supraorbital border 051 



" " malar bones 077 



" " zygomatic processes of squamosal 0795 



" of occipital condyles 031 



Elevation of occiput, including condyles 054 



Width of occiput at middle 033 



Depth skull at right angles to profile, at glenoid face. . . .046 



" orbit .049 



" " " ". " " larmier, exclu- 

 sive of teeth 044 



Depth of mandible at condyle 071 



" m. ii (middle) 025 



"P-ni. iii 022 



Length of superior dental series 0885 



" to superior P-m. i 0130 



m. i ■ 0470 



of " m. iii 0180 



" " " canine, crown 009 



" to inferior P-m. i , 012 



m. i 0425 



" of " dental series 087 



m. iii 022 



The unique and beautiful specimen on which our knowledge of this 

 species rests, was found in a formation of the Ticholeptus Miocene near 

 Laramie Peak, Wyoming Territory, by my assistant, J. C. Isaac. 



Merychyus arena rum, sp. nov. Sub-species arenarum. 



This species was more abundant than the M. leptorhynchus during the 

 Ticholeptus epoch, if we may judge from the number of specimens which 

 have been procured. I enumerate here the five most important, viz. : 

 No. 1, A skull which lacks the muzzle as far as the preorbital fossa, and 

 the palate as far as the third premolar, and which has the mandible com- 

 plete as far as the coronoid processes, and which is accompanied by fore 

 and hind feet and other limb bones. No. 2, A muzzle and right side of the 

 face including the orbit, with the entire dentition, including that of the 

 premaxillary bone, and that of the right mandibular ramus as far as the 

 second true molar inclusive. No. 3, A skull with a part of the mandible, 

 of an immature individual, in which the last superior molar is just ap- 

 pearing, and the last two temporary molars are in place, and which is ac- 

 companied by a few bones of the limbs. No. 4, Palatal part of skull with 

 nearly all the teeth,' accompanied by perfect mandible with all the teeth, 

 and a large part of the skeleton. No. 5, A skull from which the basi- 



