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, 5. hispidus, 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. 



47. Sigiuodcm. Cotton Rats. 



V. Bailey. Synopsis of North America Species of Sigmodon, 

 Proc. Biol. Soc. Wash., xv, 1902, pp. 101-116. 



Sigmodon Say & Ord, Journ. Acad. Nat. Scien. Phil., 1825, p. 352, 

 pi. xxn, 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 bullae 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 reentrant folds ; the front one has two similar 

 interior folds, the others only one each; front lower molar has two 

 exterior and three interior reentrant folds ; the last two lower molars 

 have generally but one reentrant 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 SUBSPECIES. 



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 ...................... S. alleni 224 



b." Above yellowish brown and black, 



tinged with chestnut ................ 5. h. borucce 224 



c." Above deep yellowish brown ...... S. h. chiriquensis 225 



d." Above dark reddish brown. 



a/" Beneath cinnamon brown ........ S. h. saturatus 225 



