1879.] Extinct American Rhinoceroses and their Alties. 777 
Position. —The longest known species, the A. crassus, was found 
by Dr. Hayden on the Niobrara River, Nebraska. Teeth pre- 
senting the same characters have been found in Northern Kansas 
and Eastern Colorado. The other species are more restricted 
geographically. A considerable exploration in the Loup Fork 
beds of North-eastern Colorado, conducted by myself in 1873, 
yielded four individuals of A. megalodus, but no fragments refer- 
able to the other species. Explorations in Northern Kansas by 
Russell S. Hill, of Philadelphia, produced five individuals of A. 
Sossiger and five of A. malacorhinus, but not a fragment of A. 
megalodus, 
fistory—In my original definition of this genus, I relied on 
Fic. 8.—A. malacorhinus skull, represented in Fig. 7 from above, 
one-sixth natural size. 
the number of premolars in distinguishing it from Rhznocerus 
as well as on the absence of the horn. These teeth are generally 
3 in Aphelops, and are said to be # in Rhinocerus, in most works, 
on the subject. These numbers are not constant; on one side of 
both jaws in Aphelops from Colorado, I have observed a first pre- 
molar, and on one side of the upper jaw of A. malacorhinus there 
are four premolars ; the other side is injured. In several species 
of Rhinocerus, three premolars only are usually found in the 
mandible. I may add that Lesson and Peters! have described a 
Rhinocerus tnermis Less., which is found living on some of the 
islands at the mouth of the Ganges. The only known specimens 
are the skulls, with portions of the skin, of a female and young. 
These are hornless, and in general structure allied to the A. son- 
daicus, yet presenting some important differences? Should the 
characters of this form prove to be specific, and the male be 
found to lack the horn, it must be regarded as a species of 
Aphelops. 
2 Monatsberichte Berlin. Akademie, 1877, p. 68, pl. 1-2. 
2 Peters represents the posttympanic as not codssified below the meatus as in 2. 
sondaicus. 
