1918] Taylor: Revision of the Rodent Genus Aplodontia 447 
C. HISTORY OF THE APLODONTIIDAE 
1. GENERAL REMARKS 
This family is exclusively North American in origin, development, 
and present distribution. In the absence of any other evidence of 
European relationship it is probable that the resemblances noted 
between the American Oligocene aplodontid genus Allomys and the 
genus Sciurodon of the European Oligocene (see Schlosser, 1884, pp. 
73, 136) are indicative of accidental convergence rather than real 
relationship. 
The earliest aplodontid genius is Allomys Marsh (1877, p. 253) or 
Meniscomys Cope (1878, p. 5). Found typically in the Oligocene 
deposits of the Middle John Day in Oregon, there is only a single 
record, so far as known to the writer, of its occurrence elsewhere, 
that of Matthew (1904, p. 263), who has recovered an undetermined 
species from the Lower Miocene of South Dakota. 
The members of the genus Allomys were small, ranging from one- 
half to two-thirds the size of Recent Aplodontia. They were much 
more squirrel-like than is the Recent genus. 
Founded upon a single specimen, an imperfect cranium without 
lower jaws, taken in the gravels and tuffs at the top of the Upper 
John Day, Mylagaulodon is one of the most interesting of the genera 
which are associated with the Aplodontiidae. The characters of the 
fourth premolar and infraorbital region of this genus are regarded as 
demonstrating its aplodontid position. * 
The earliest known fossil remains of the genus Aplodontia were 
found by parties from the University of California in the Virgin 
Valley Miocene and Thousand Creek Pliocene of northern Humboldt 
County, Nevada. The species there recovered is known as Aplodontia 
alexandrae Furlong (1910, pp. 397-403). It is somewhat smaller than 
the Recent members of the genus, and differs from them in several 
particulars, the most important beimg the relative position of the 
prominent style internally on the lower molars. For all that, one is 
impressed with the resemblances rather than the differences between 
the Tertiary Aplodontia alexandrae and the Recent species of the 
genus. 
Another species of Aplodontia has recently been described by Dr. 
J. C. Merriam (1916, pp. 177-179) from the Cedar Mountain region 
of western Nevada. The formation in which the specimen (a single 
