158 BULLETIN 18 7, UNITED STATES NATIONAL MUSEUM 



Type locality. — "Mexican plateau between the eastern range and the 

 Valley of Mexico." 



Range. — Southern portion of the central plateau, from southern San 

 Luis Potosi south to central Puebla, and west to Jalisco; also the 

 Sierra Madre del Sur, Guerrero (recorded from numerous localities 

 in the states of Durango, Guerrero, Guanajuato, Jalisco, Mexico, 

 Morelos, Puebla, and San Luis Potosi, and from Distrito Federal). 



Genus THAMNOPHIS Fitzinger 



Thamnophis Fitzinger, Systema reptilium, 1843, p. 26. — Smith, Zoologica, vol. 

 27, 1942, pp. 97-123 (brief notes on Mexican species). 



Prymnomiodon Cope, Proc. Acad. Nat. Sci. Philadelphia, 1860, p. 558 (type, P. 

 chalceus Cope). 



Chilopoma Cope, in Yarrow, Wheeler's Rep. Geogr. Geol. Expl. Surv. W. 100th 

 Mer., vol. 5, Zool., 1875, p. 543 (type, C. rufipunctatum Cope). 



Atomarchus Cope, Amer. Nat., vol. 17, 1883, p. 1300 (type, A. rmiltimaciilatus 

 Cope). 



Btypocernus Cope, Proc. Amer. Philos. Soc, vol. 22, 1884 (1885), p. 387 (substi- 

 tute name for Chilopoma, preoccupied; type, C. rufipunctatum Cope). 



Genotype. — Coluber saurita Linnaeus. 



Range. — Southern Canada to Costa Rica. 



Species. — About 46 species and subspecies, 29 in Mexico. 



KEY TO MEXICAN AND CENTRAL AMERICAN FORMS OF 

 THAMNOPHIS 



1. Lateral stripe involving third and fourth scale rows on anterior part 



of body 2 



Lateral stripe not involving fourth row, or indistinct, absent, or involving 

 only the second or third row or both 5 



2. Scale rows 21 at middle or on anterior third of body ; anterior edges 



of ventrals black macrostemma 3 



Scale rows 19, maximum (except immediately behind head) 4 



3. Caudals 78 or less in males, 68 or less in females. 



macrostemrQa macrostemina 

 Caudals 79 or more in males, 69 or more in females- macrostemma meg'alops 



4. Caudals 93 to 104, ventrals 155 to 169, totals 255 to 262 in females; 



102 to 109, 158 to 172, and 260 to 277, respectively, in 



males sauritus proximus 



Caudals 83 to 96, ventrals 142 to 159, totals 229 to 254 in females ; 92 

 to 99, 149 to 158, 245 to 256, respectively, in males sauritus chalceus 



5. Scale rows 21 or more on anterior third of body 6 



Scale rows less than 21 14 



6. Preoculars two or more; one or two labials entering orbit 7 



Preocular single; usually two labials entering orbit 9 



7. One labial entering orbit (rarely 2) rufipunctatus 



Two labials entering orbit 8 



