98 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
HESPEROMYS CALIFORNICUS, (Gambel) Baird. 
Parasitic Mouse. 
Mus californicus, GAMBEL, Proc. Acad. Nat. Sci. Phila. iv, 1848, 78 (Monterey). 
Hesperomys californicus, Batrp, M. N. A. 1857, 478 (Santa Clara County, Cal.). 
Hesperomys ( Vesperimus) californicus, Cours, Proc. Acad. Nat. Sci. Phila. 1874, 180. 
Hesperomys parasiticus, COOPER, MSS.—BatrD, op. cit. 479 (in text). 
Dracnosis.—H. crassitie dimidium muris decumantis subequans, cauda lon- 
gissimd subnuda vix bicolore, pedibus uncialibus plantis nudis, auriculis maxi- 
mis sparsissimée pilosis; supra fuscus, lateribus sensim flavicantibus, infra 
albidus. 
Nearly as large as a half-grown house-rat, with extremely long nearly 
naked ears and tail, the latter scarcely bicolor; feet an inch long, with naked 
soles; dark grayish-brown above, becoming pale cinnamon-brown on the 
sides, the under parts whitish. 
Hasrrat.—Southern and Lower California. 
Our few specimens, mostly the same as those described by Baird in 1857, 
indicate a species perfectly distinct from deucopus. The animal looks, in fact, 
much like a partly-grown Neofoma ; it is quite as large as some examples of 
Oryzomys palustris, while its long and sparsely hairy tail, no less than its 
size, gives it somewhat the aspect of a young Norway rat. No one of the 
interminable variations of /ewcopus have so far shown us anything like this. 
The size and proportions of the species are illustrated in the table given 
below. It may be said to be four or five inches in length of trunk, with 
the tail about the same—half an inch longer or as much shorter than the 
head and body. The feet are an inch or a little more long, and share with 
eremicus the peculiarity of naked soles, although the very extremity of the 
heel is not perfectly denuded. The immense ears are a striking feature, 
measuring three-fourths of an inch or more if height by about two-thirds of 
an inch in width. They are very closely pilous on both sides, as will be seen 
by close inspection, but appear at first sight quite naked. The little hairs are 
so short that they do not form any perceptible fringe. The shape of the ear 
is also remarkable; instead of being evenly rounded, it is like the two sides 
of a rectangle with the upper corner rounded off. The tail is scant-haired, 
showing the annuli plainly. . 
The pelage is remarkable for its softness, fullness, and gloss, although it 
is not long, measuring less than half an inch on the back. It is very different 
