FAMILY MURID^. 91 



A. nuttali. (Harlan, Med. and Phys. Res. p. 55, plate.) Fawn color above, white beneath; ears 



large and hairy. Tail nearly as long as the body. Length 5i inches. Virginia. 

 A. pinetorum. (Le Conte, Ann. Lye. Vol. 3, p. 132, plate.) Dark ash, tipped with brown; ears 



short, naked, concealed ; thumb with a straight nail. Tail round, • 7 long. Length 3 to 4 inches. 



Georgia. 

 A. gapperi. (Zool. Joum. Vol. 5, p. 202.) Tail more than half the length of the body; ears short, 



rounded, chesnut above ; face and sides yellowish brown ; belly yellowish white ; chin and throat 



ashen. Tail nearly two inches. Length six. An neoboracensis ? 

 A. ferrugineus. (Harlan, Med. and Phys. p. 57.) Rust-colored above, white beneath; fore legs 



short. Tail more than half the length of the body. Length 11 inches. Mississippi. 

 A. richardsoni, (riparius of Richardson, p. 120.) Dull browTi mixed with black, bluish grey beneath; 



ears moderate, nearly concealed. Tail flat, as long as the head ; feet white. Length 9 inches. 



Arctic Regions. 

 A. nibricatus. (Beechey's Appendix.) With a bright red stripe on the flanks. Behring's Straits. 



Genua Neotoma, Say and Ord. Molars with large roots ; the folds of the enamel not descending as 



low as the edge of the alveolar processes. Its other characters similar to the genus Arvicola. 

 N. floridanum. (Ac. Sc. Vol. 4, p. 345, pi. 21.) Plumbeous above, yellowish on the sides; eyes and 



ears very large. Tail longer than the body. Length 14 inches. Florida. 

 N. drtimmondi. (Richardson, pi. 7.) Yellowish brown above, white beneath. Tail more bushy 



towards the extremity, longer than the body. Length 16 inches. Rocky Mountains. 



Genus Sigmodon, Say. Molars subequal, with roots ; the folds of the enamel representing the letter S. 

 S. hortense. (Harlan, Med. and Phys. pi. Ac. Sc. Vol. 4, pi. 22.) Soiled yellow or blackish above, 



beneath cinereous ; ears large and round. Tail nearly as long as the body. Length 10 inches. 



Florida. 



Genus Georychus, Illiger. Eyes very small; ears rising slightly above the auditory hole ; thumb 



obvious ; toes of the fore feet formed for digging. Tail very short. 

 G. helvolus. (Richardson, p. 128.) Head black and tawny; body reddish orange, paler beneath. 



Length 5 inches. Northern Regions. 

 G. trimucronatus. (Richardson, p. 130.) Chesnut above ; thumb nail with three projecting points. 



Length 5^ inches. Arctic Regions. 

 G. hvdsonius. (Id. p. 132.) Dark brown above, bright rusty on the sides; the two middle nails of 



fore feet very large, with a deep notch on the ends ; earless. Length 6 inches. Labrador and 



Arctic Regions. 

 G. graynlandicus. (Id. p. 134.) Earless; a dark dorsal stripe; nails of the fore feet terminating in 



sharp cylindrical points. Length 7 inches. Arctic Regions. 



Genus Aplodontia, Richardson. Molars ten above, eight beneath; ears short and round; feet five- 

 toed ; nails large, strong and compressed. Tail minute, concealed by the fur. 

 A. leporina. (Richardson, p. 211, pi. 18.) Umber brown above, greyish beneath ; legs short; throat 

 with a white spot, Tail J an inch. Length 1 4 inches. Northern Regions, Missouri. 



