56 MEMOLRS OF THE CARNEGIE MUSEUM 
Professor Cope points out the ‘“close-placed premolar teeth” and the elevation 
of the anterior tubercles “ of the true molars as a more primitive character than is 
displayed by any of the American species so far known. ‘To this may also be added 
the abrupt reduction of Py, which, though distinctly smaller than in A. mortoni, 
is, however, again repeated in Dinohyus from the Miocene. The latter has P; 
and Ps of very nearly the same relative size as in Archxotherium coarctatum. ‘The 
Fia. 11. Type of Archxotherium coarctatum Cope. About } nat. size. (After Cope. ) 
development of the posterior tubercles on Mz of the latter species seems to indicate 
a slight advance in modification toward the later forms, Dinohyus and Ammodon, 
while in the typical forms of A. mortoni these tubercles are less developed. 
Subgenus PELONAX Cope. 
Pelonax ramosum Cope. 
Type: The greater part of a mandible. 
Horizon: Upper Oligocene ? 
Locality: Eastern Colorado. 
Locality of Type: The American Museum of Natural History. (Cope Collec- 
tion, No. 6393.) 
In the original description (7, p. 27) of the subgenus Pelonaa Professor Cope 
enumerates strong specific characters, viz.: the “great size of the tubercles on the 
under side of the mandibular ramus, especially the anterior pair . . . the first and 
‘4 1t should be carefully borne in mind that all the species known from the lower Oligocene beds have the an- 
terior cusps of the molars higher in a greater or less degree. 
