MAMMALS OF THE MEXICAN BOUNDARY. 339 



are so intimately connected with (lit- preceding subfamily (Sciurinm) 

 that the division into two groups is purely a matter of convenience. 

 They are confined to the Palsearctio and Nearctic regions. ( Flower arid 

 Lydelcker.) 



Genus CYNOMYS Rafinesque (1817). 



Five distinct claws to each fool, that on the thumb as large as that 

 on the fifth toe. Cheek-pouches shallow. Ear-conchs small. Tail 

 short. Skull stout, with postorbital process strongly developed and 

 directed outward. Dentition as shown in fig. 56. First premolar 

 nearly as large as the second. Lateral rows of teeth strongly con- 

 vergent posteriorly and twisted on their axis. Incisor teeth white or 

 hut slightly colored. Mammas, four or live pairs. Form stout and 

 muscular. 



Two species of this genus inhabit the region of the Mexican Border. 

 Their ranges are complementary, Cynomys ludovieianus arizonensis 

 being an inhabitant of the Sonoran Life Zone, on both sides of the 

 International Line, while ( '. gunnisoni is restricted to the Transition 

 Zone, its range to the southward falling short of the Mexican Boundary. 



CYNOMYS LUDOVICIANUS ARIZONENSIS (Mearns). 

 ARIZONA PRAIRIE-DOG. 



( ynomys arizonensis Mearns, Bull. Am. Mua. Nat Hist., II, No. 4, Feb. 21, L890, 

 p. 305 (original description). — Allen, Bull. Am. Mus. Nat. Hist., VII, L895, 

 p. 237.— Miller and Rehn, Proc. Boat. Soc. Nat. Hist., XXX, No. 1, Dec 27, 

 1901, p. 57 (Syst. Results Study N. Am. Mam. to close of 1!>00). 



[Qynomys'] arizonensis, Elliot, Field Col. Mus.,Zool. Ser., II, L901 (Synop. .Mam. 

 X. Am.); IV, 1904, p. 154 (Mam. Mid. Am.). 



Cynomys ludovieianus arizonensis, Merriam, Proc. Biol. Soc. Wash., VII, |>. 158, 

 July 27, 1892. 



Type-locality. — Point of Mountain, near Willcox, Cochise County, 

 Arizona. (Type, No. ^W, American Museum of Natural History. 

 New York.) 



Geographical range. — Grassy plains of the Sonoran Zone, from the 

 Pecos River, Texas, west to the \ alley of the San Pedro River, Arizona. 



Description. —Largest of the prairie-dogs found in the United States.' 2 

 Length, 400 mm.; tail vertebras, ( .'<»; hind foot. 64; head. 73. Skull, 

 66 by 47»: incisors white or slightly colored. Mammae 4 pairs (A j, 

 P. 1 . A. ] . 1. {). In winter the pelage of the upper surface is pale sandy 

 buff, with a few all-black and many gray-tipped hairs; under surface 

 white or pale yellowish; sides yellow; (ail with a narrow, subterminal 

 bar of black; under side of tail and inguinal region taw ny ochraceous; 

 underfur copious. In summer the underfill- i- wanting; color vinace 

 ous cinnamon above, with but few black hairs and grizzling obsolete; 

 below whitish; sides yellowish. Iris hazel. 



" The ( ynomys mexicanus of Merriam, Erom La Ventura, < toahuila, Mexico, is about 

 the same size, l>ut has a much Longer tail. 



