15 



In the inferior molars the two median interior tubercles are stout, and 

 the loops which they hound, are nearly enclosed. There is a tubercle be- 

 tween the bases of the external columns. 



Measurements. M. 



Length of crown of superior molar 028 



t\- , • i I anteroposterior 018 



Diameter superior molar 1 



I transverse 016 



Long diameter internal column-lake 005 



From the Pliocene formation of Cottonwood, Grant co., Oregon. 

 D^eodon shoshonensis, gen. et sp. nov. 



Ge?i. Cliar. These are indicated by the terminal portion of the lower 

 jaw of a huge mammal, which does not resemble that of any known 

 genus of this order. It supports on the side, three incisors, one canine, 

 and two premolars, which form an uninterrupted series. The first pre 

 molar has two roots ; and the canine is of huge proportions. The mandib- 

 ular symphysis is coossified, and there are no osseous tuberosities on it 

 nor on the adjacent parts of the rami. 



The characters of the piece on which this genus is established indicate 

 that the latter probably pertains to the ChalicotheriicM along with Menodus 

 and Symborodon. From these its six inferior incisors distinguish it, while 

 the absence of a diastema separates it from Chalicotfierium. From Palce- 

 osyops and Limnohyus it may be known by the large two-rooted first pre- 

 molar, or more correctly, in all probability, by the absence of the first 

 premolar of the inferior series. In the relatively powerful canines it re- 

 sembles the last named rather than the first named genera. 



Specif. Char. The canine teeth are very robust, as in the species of 

 Elotlierium. The inferior face of the symphj^sis is not steeply inclined, 

 and is quite elongate. It is narrowed near the bifurcation and expands to 

 a rounded incisive border. The first incisor is narrower than the second 

 and third, which are robust. There are two small mental foramina, the 

 larger below the anterior root of the anterior premolar ; the second below 

 the anterior root of the second premolar. 



Measurements. M. 



Length of symphysis above 155 



Width between bases of canines 100 



Antero-posterior diameter of base of canine 055 



Transverse " " second incisor 022 



-r.. . e , ~ j. . t (antero-posterior 040 



Diameter of base of first premolar ; ' 



1 transverse 025 



This species is the largest of the North American Perissodactyla, with 



the possible exception of the Menodus proutli. 



AUTIODACTYLA. 



Hyopotamus guyotianus, sp. nov. 



This species of a genus little known in North America, is represented by 



