1918 | Taylor: Revision of the Rodent Genus Aplodontia 449 
Reference has already been made to the conservatism of the aplo- 
dontid phylum. If, as seems highly probable, Aplodontia alerandrac 
is near the direct line of descent of the recent species, it is noteworthy 
that, during a lapse of time sufficient for the evolution of the horse 
from the Miocene MWerychippus type to the larger Pliocene Pliohippus, 
there was no great specific change; and that, during a time which 
sufficed to transform the short-toothed, small-sized Merychippus ito 
the much larger modern Equus, with modifications in every bone in 
the body, and with characters generically probably twice removed, the 
aplodontid stock has undergone comparatively slight change, all 
Fig. E. Continent of North America, to indicate present range of genus 
Aplodontia, and apparent extension of range of family Aplodontiidae in Tertiary 
times. 
Cross-hatehed area indicates limits of range of Recent genus; cirele represents 
record of fossil genera Allomys and Mylagaulodon; triangle indicates an addi- 
tional record of Allomys; squares indicate records of genus Aplodontia fossil. 
