15 
In the inferior molars the two median interior tubercles are stout, and 
the loops which they bound, are nearly enclosed. There is a tubercle be- 
tween the bases of the external columns. 
Measurements. ; M. 
Length of crown of superior molar. ...........2.0-005 .028 
Diameter superior molar f antero-posterior. ..........- -018 
(transverse. 0.6... 0022s eee .016 
Long diameter internal column-lake................05. 005 
From the Pliocene formation of Cottonwood, Grant co., Oregon. 
DoOpON SHOSHONENSIS, gen. et sp. nov. 
Gen. Char. 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 coédssified, 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 Chalicotheritde along with Menodus 
and Symborodon. From these its six inferior incisors distinguish it, while 
the absence of a diastema separates it from Chalicotherium. From Pale- 
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 Jast named rather than the first named genera. 
Specif. Char. The canine teeth are very robust, as in the spccies of 
Hlotherium. The inferior face of the symphysis 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............. 2. sce eee eens 155 
Width between bases of canines............. 0.0 cece 100 
Antero-posterior diameter of base of canine............ 055 
Transverse ef ee second incisor..... .022 
: . antero-posterior.... .040 
Diameter of base of first premolar { T i 
 transverse......... -025 
This species ig the largest of the North Amcrican Perissodactyla, with 
the possible exception of the Menodus proutit. 
ARTIODACTYLA. 
HYoPoTAMUS GUYOTIANUS, Sp. nov. 
This species of a genus little known in North America, is represented by 
