CHECKLIST OF THE SNAKES OF MEXICO 71 



GYALOPION CANUM Cope 



Gyalopion canum Cope, Proc. Acad. Nat. Sci. Philadelphia, vol. 12, 1860, p. 243. — 

 Smith and TAYiiOE, Journ. Washington Acad. Sci., vol. 31, 1941, pp. 361-362, 

 figs. 1, 6, 16 (head scales), map fig. 17. — Smith, Publ. Field Mus. Nat. Hist, 

 zool. ser., vol. 29, 1944, pp. 139-140. 



ry;>e.— U.S.N.M. Nos. 16427-8, two cotypes. 



2'^pe locality. — Fort Buchanan, Ariz. 



Range. — Southeastern Arizona east to Tom Green County, Tex., 

 and southward at least to the Chisos Mountain area in the Great Bend 

 of the Rio Grande in western Texas, and probably into northern 

 Chihuahua and Coahuila (known in Mexico only from near Galeana, 

 Nuevo Leon). 



GYALOPION DESERTORUM (Taylor) 



Ficimia descrtorum Taylor, Proc. Biol. Soc. Washington, vol. 49, 1936, pp. 51-52; 



Univ. Kansas Sci. Bull., vol. 24, 1936 (1938) , p. 494, pi. 43, fig. 1 (photograph). 

 Gyalopion desertorum Smith and Taylor, Journ. Washington Acad. Sci., vol. 31, 



1941, p. 359, tigs. 2, 7, 15 (head scales), map fig. 17. 



Type.—E. H. Taylor-H. M. Smith Coll. No. 4576. 



Type locality. — Twelve km. northwest of Guaymas, Sonora. 



Range. — Kjiown only from the type locality. 



GYALOPION O.UADRANGULARIS (Gunther) 



Ficimia quadra ngularis Gunther, Biologia Centrali-Americana, Kept., 1893, 



p. 99, pi. 35, fig. A. 

 Oyalopion quadrangularis Smith and Taylor, Journ. Washington Acad. Sci., vol. 



31, 1941, pp. 359-361, map fig. 17. 



Type. — Brit. Mus. Nat. Hist. 



Type locality. — Presidio, near Mazatlan, Sinaloa. 



Range. — Known only from the type locality. 



Genus HETERODON Latreille 



Heterodon Latreille, in Sonnini and Latreille, Histoire naturelle des reptiles, 

 vol. 4, 1802, p. 32. 



Genotype. — Heterodon platyrhinos Latreille. 



Range. — New Hampshire west to Montana and southward through 

 all the Gulf States and northern Mexico. 



Species. — Four, one occurring in Mexico; the Mexican species is 

 represented by two subspecies. 



KEY TO MEXICAN FORMS OF HETERODON 



1. Accessory scales (excluding azygous) 2 to 6; loreal usually single or 



absent nasicus kennerlyi 



Accessory scales 8 to 19; loreals usually 2 to 5 nasicus nasicus 



HETERODON NASICUS NASICUS Baird and Girard 



Heterodon nasicus Baird and Girard, in Stansbury's Exploration and survey of 

 the Valley of the Great Salt Lake of Utah, 1852, pp. 352-353.— Van Denbtjbgh, 



