Cope.] -»4: [May 16, 



A portion of a left maxillary bone supporting the true molars of a horse 

 from the Oregon desert, received from Professor Condon, resembles closely 

 the type specimen from Nebraska described by Leidy as above. Two 

 skulls, in the two museums of Mexico already referred to, present the same 

 dental characters. In identifying the Mexican with the Oregon and Ne- 

 braska horses, I wish to be understood as making a provisional arrange- 

 ment only, for unfortunately the cranium of the North American horse 

 with this dentition is yet unknown. The uncertainty attending a dental 

 identification being admitted, I proceed to the description. 



This species differs from the others, whose remains have been found in 

 the valley of Mexico, in the elongate and flattened form of the lobe formed 

 by the section of the anterior internal column of the superior molar. This 

 long diameter generally exceeds the half of that of the crown of the 

 tooth by one-eighth the latter, and is rarely so short as one half of the 

 same. The loops of the lakes are few, including only one near the pos- 

 terior borders near the internal side and one on the anterior border of the 

 posterior lake. There is generally a little loop at the notch belween ilie 

 two internal lobes. Crowns straight, second superior premolar elongate 

 and acute. 



One of the crania is complete, lacking only the lower jaw, and the two 

 third true molars. The other lacks all posterior to the palatal notch. 

 From the former I derive the following characters : 



The apex of the nasal bones is above the superior canine tooth. The 

 posterior border of the nares marks the middle of the anterior column 

 of the third premolar. The infraorbital foramen is above the posterior 

 edge of the second column of the fourth premolar. There are two notches 

 on the anterior part of the superciliary border ; and there is a short exos- 

 tosis on each side of the front, in line with the supraorbital border, in 

 front of the preorbital border. 



Measurements. M. 



Length from superior edge of foramen magnum to in- 

 cisive border 565 



From posterior nares to incisive border 300 



Interorbital width 166 



Length of series of molar teeth , 191 



" precanine diastema 022 



" postcanine " 056 



Width of palate at third incisors 092 



" " canines, inclusive 075 



Diameters P-m. ii ' anteroposterior 0425 



i- transverse 02 



Diameters P-m. iii 



anteroposterior 032 



transverse 034 



Diameters M. iii \ anteroposterior 0335 



( transverse 029 



