26 



61. Hemipenis with a single basal hook in basal third of organ T. r^licta 



Hemipenis with two basal hooks, one in basaJ third of organ and the other 



in mesaJ third 62 



62. Prominent pale nuchal band present, usually 3 or fewer scales in length at 



dorsal midline T. coronaia 



No prominent pale nuchal band usually present, if so, broken middorsally and usually 

 confined to scales posterior to parietals T. oolitica 



63. Pale nuchal band distinct, bordered behind by dark nape band 64 



Pale nuchal band distinct or not, not bordered posteriorly by dark pigment, or, if so, 

 pigment reduced to series of spots ~ - 65 



64. Pale nuchal band complete; subcaudals 38-63 T. bocourti (part) 



Pale nuchal band indistinctly to completely medially divided; subcaudals 63-83 



- T. cucullata (part) 



65. Black head cap does not extend laterally below angle of mouth T. hobartsmithi 



Black head cap extends laterally below angle of mouth — ~ 66 



66. Extensive white postocular spot present, extending onto lower one-fourth to 



three-fourths of anterior temporal — T. yaquia 



No white pigment on anterior temporal T. planiceps 



Distributional Commentary 



The genus Tantilla is distributed from southern Virginia, southern Indiana, southwestern 

 Illinois, southern Missouri, southwestern Nebraska, Kansas, eastern and extreme western 

 Colorado, southern Utah, southern Nevada, and southern California, south through the 

 peninsula of Baja California, and the large majority of mainland Mexico, throughout Central 

 America, and into South .Ajnerica as far south as southern Peru, Bolivia, northern Argentina, 

 and Uruguay. The genus is also distributed on Isla del Carmen in the Gulf of California, the 

 Tres Marias Islands off the Pacific coast of mainland Mexico, the Bay Islands of Honduras, and 

 Trinidad and Tobago in the British West Indies. 



Four major regions, thus, are inhabited by species of Tantilla (Table 1). They are the United 

 States, Mexico, Central America, and South America. The United States is occupied by 1 1 

 species in the genus (Table 1). Three of these species {T. coronaia, T. oolitica, and T. relicta) 

 are distributed east of the Mississippi River Valley. The remaining eight species {T. atriceps, T. 

 cucullata, T. gracilis, T. hobartsmithi, T. nigriceps, T. planiceps, T. wilcoxi, and T. yaquia) 

 occur largely west of the Mississippi River Valley. The only species of western U.S. Tantilla 



