222 SIGMODON. 
SIGMODON contains the well-known Cotton Rats of the Southern 
States and Mexico. They have a coarse, grizzled coat, harsh in feel- 
ing, and a bicolor tail. There is a very close general resemblance 
between the longest known species, S. jispidus, and the several races 
that have been separated from it, and they are not always easy to 
be distinguished, especially if the locality of a specimen is unknown. 
They are rather short, thickset animals, about half the size of a fully 
grown house rat, and are often found in large colonies in the localities 
they frequent. 
4%. Sigmodon. Cotton Rats. 
2 2 
ais 6 6)e 
US 4 
i ) . = 
V. Bailey. Synopsis of North America Species of Sigmodon, 
Proc. Biol. Soc. Wash., xv, 1902, pp. ro1—116. 
Sigmodon Say & Ord, Journ. Acad. Nat. Scien. Phil., 1825, p. 352, 
pl. xxl, figs. 5-8. 
Skull short and wide, length less than twice the zygomatic width; 
rostrum short, swollen; superior outline of skull arched; pointed 
process of lamellar plate of maxillary nearly dividing the lower part 
of the antorbital foramen from the upper; an azygos median process 
on palatal arch; prominent bead on the supraorbital border extending 
obliquely backwards to occiput; audital bulla small; upper molars 
three-rooted; front lower molar four-rooted; second and third lower 
molars three-rooted; sometimes minute accessory fangs are present; 
upper molars with two reéntrant folds; the front one has two similar 
interior folds, the others only one each; front lower molar has two 
exterior and three interior reéntrant folds; the last two lower molars 
have generally but one reéntrant lobe on each exterior and interior 
side; pelage coarse, bristly; form stout; tail generally shorter than the 
body; ears large; front feet small; hind feet very long, soles naked. 
KEY TO THE SPECIES AND SUBSPEGIES: 
A. Tail nearly bare. 
a. Size small; hind foot less than 32 mm. PAGE 
a.’ Under parts grayish or buffy white. 
a.’ Above dull tawny...............2. <. 3. 6S 
b.’” Above yellowish brown and _ black, 
tinged with chestnut................ 5: /abonn@e=ee 
c.’’ Above deep yellowish brown....... S.h. chiriquensis 225 
d.’’ Above dark reddish brown. 
yer 
a.’’’ Beneath cinnamon brown........S. h. saturatus 225 
