298 BULLETIN 56, UNITED STATES NATIONAL MUSEXTM. 



The ground squirrels of the United States and Mexican Boundary 

 region may be determined by means of the following: 



KEY TO GEODND-SQUIEBELS FOUND ON THE MEXICAN BOUNDAHY LINE, BASED ON EXTERNAL 



CHARACTERS. 



o. Above longitudinally striped, or spotted in longitudinal series, forming inter- 

 rupted stripes. 

 h. Stripes continuous, 

 c. Witli one white stripe on each side. 

 d. Tail white below. 

 e. Caudal hairs with one free black band. 



Ammospermophilus leucurus (p. 299) 

 ■ee. Caudal hairs with two free black bands. • 



Ammospermophilus leucurus interpres (p. 301) 

 dd. Tail iron gray below. 



f. Coloration dark ; length of caudal vertebrae, 80 mm. 



Ammospermophilus harrisii (p. 303) 

 ff. Coloration pallid ; length of caudal vertebrae, 95 mm. 



Ammospermophilus harrisii saxicola (p. 306) 

 cc. With three stripes on each side, one white and two black. 

 g. Tail all grayish or viuaceous above. 



Callospermophilus lateralis (p. 309) 

 Off. Tail with terminal half black above. ' 



Callospermophilus lyernardinus (p. 313) 

 66. Stripes interrupted, composed of lines of spots or of stripes containing 

 rows of spots. 



h. Larger ; length more than 280 mm. 

 7. Color olivaceous gray ; tail flattened, long, and bushy. 



Gitellns (Ictodom'oicles) mexicanus parvidens (p. 328) 

 a. Color soiled yellowish; tail subcylindrical, with rather short 

 hairs. 



Gltellus (Ictidomys) tridecemlineatus texensis (p. 327) 

 hli. Smaller ; length less than 280 mm. 

 j. Upper surface pale grayish brown. 



Oitellus ( Xerospermophilus) spilosoma annectens (p. 332) 

 jj. Upper surface russet or viuaceous cinnamon. 

 h: Color pallid ; spots small. 



Citellus (Xerospermophilus) spilosoma arens (p. 331) 

 klc. Color dark ; spots large. 

 Citellus (Xerospermophilus) spilosoma macrospilotus (p. 333) 

 aa. Above not distinctly striped or spotted in longitudinal series. 



/. Form squirrel-like ; ears high ; tail flattened and bushy. 

 m. Smaller ; length, 410 mm. ; tail, 170 ; hind foot, 55. 

 A triangular patch of 'silver gray above shoulder; 

 six pairs of mammary teats. 



Otospermophihis heechepi (p. 324) 

 mm. Larger ; length, 490 mm. ; tail, 220 ; hind foot, 62. 

 No triangular patch above shoulder ; five pairs of 

 mammary teats. 

 «. Color of mantle grayish. 



Otospermophihis grammurus (p. 315) 

 nn. Color of mantle black. 



Otospermophihis grammurus iuckleyi (p. 323) 

 U. Form weasel-like ; ear-conch minute ; tail terete. 



Citellus (Xerospermophilus) tereticaudus (p 336) 



