1883.] The Extinct Rodentia of North America. 165 
ON THE EXTINCT RODENTIA OF NORTH AMERICA. 
BY PROFESSOR E, D. COPE. 
Miocene RODENTIA. 
(Continued from page 57.) 
Eumys (Leidy) Cope. 
With this genus we commence an account of the mice of Mio- 
` cene times. Representatives of this primary division were not as 
numerous during this period in North America as they are at the 
present epoch, and very few of them sag the apne type of 
molar teeth, as do the Arvicola or 
meadow mouse, and muskrat, genera 
of later periods. In Eumys we have 
the predecessor of our wood-rats and 
mice, but which unites with some den- 
tal characters of these animals, the 
cranial form of Fiber or the muskrat. 
The molar teeth are tubercular, with 
alternating lobes as in Hesperomys 
(wood-mouse), but there are interme- 
diate cross-crests on the inner side of 
the lower, and outer side of the upper 
jaws, so that when worn, the _crowns 
present exactly the pattern of Gym- 
noptychus. There are no ridges 
bounding the orbits above, and there Y 
i i 5 ore - 
PSR ce STENCIL Scan cee ote 
ittle worn molars. Twice natural 
entia, retained in the Arvicoles and ee From rete White Rive aot oe ated 
muskrats, U.S. Gablagien) Surv. Terrs 
But one species is known, the Eumys elegans Leidy. It is only 
found in the White River beds of Nebraska and Colorado. It was 
as large as a Pennsylvania meadow-mouse, and must have been 
exceedingly abundant. See Figs. 13-14. 
HEsPERomys Waterhouse. 
This existing genus is represented by a species (H. nematodon 
