212 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
a 
These colors fade on the sides, without any tangible dividing line, into 
the peculiar shade of the whole under parts. In an average case, the belly 
shows a background of plumbeous, strongly washed over with a dirty cin- 
namon, or muddy rust color. In the darkest-colored individuals, the under 
parts are deep hoary-plumbeous, with the tips of most of the hairs barely 
touched with muddy; this peculiar shade, so different from the clear hoary- 
plumbeous of riparius, &c., being a strong mark of the subgenus, and only 
very exceptionally wanting. In the lightest-colored specimens, on the other 
hand, the under parts are so strongly invaded with the muddy cinnamon that 
the plumbeous bases of the hairs are scarcely visible, the dirt-color being 
continuous, especially along the sides, and so bright as to approach a fawn- 
color or tawny-brown. 
The tail is almost always distinctly bicolor, and it shares the colors of 
the upper and under parts of the body respectively. 
The type of the species (No. 2249, Mus. Smiths.) is a rather unusually 
dark specimen, especially underneath, being, as Professor Baird has remarked, 
one of the few in which the cinnamon tips of the hairs are inappreciable. 
Other specimens, however, received from Major LeConte as typical of his 
species, have the muddy wash very distinct. 
The Louisiana specimen enumerated by Professor Baird (No 743%, Cal- 
casieu Pass, G. Wiirdemann) is typical austerus, and extends the known range 
of this form. A Kansas example (No. 4218, Neosho Falls, B. F. Goss) is 
likewise pure austerus. Another Kansas specimen (No. 3306, Doniphan 
County, E. Palmer) leans rather over against var. curtatus in the shortness 
of its tail, though it is typical awsterus in other respects. A Platte River 
specimen (No. 8004) is identical with the type of ‘‘haydent”. The exact 
state of the case regarding this last is given beyond; here it only remains to 
examine the other nominal species that has been referred to austerus. 
The type and only known specimen of ‘‘cinnomomea” (No. ¥7's, 
Pembina, Minn.) is, as Professor Baird says, exactly like awsterus in external 
characters. The points of difference, if any, lie in the skull and teeth; and 
we have thé data to show that the slight differences observable in these 
respects are quite within the limits of individual variation. On coming into 
our hands, the skull lacked zygomata; but the zygomatic width is stated by 
Professor Baird to have been 0.56, which, with a length of 1.12, gives a 
proportion of just 100 : 50, which is a little greater length for breadth than 
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