Vol. VIII] VAN DENBURGH AND SLEVIN— GARTER-SNAKES 183 



The seven kinds of garter-snakes recognized in the earlier 

 study are here increased, through the recognition of additional 

 subspecies and the inclusion of the snakes of Arizona, to 14 

 species and subspecies. As regards the original area, however, 

 the increase is three subspecies. 



Excepting certain species from Arizona, all of our garter- 

 snakes may be regarded as belonging to two groups or lines 

 of descent. These may be spoken of as the sirtalis and elegans 

 groups. The latter" is much the larger. We are unable to fol- 

 low Ruthven in placing in it Thamnophis angustirostrisj but 

 otherwise include about the same forms. 



LIST OF SPECIES AND SUBSPECIES 



These snakes usually may be distinguished by the characters 

 set forth in the following "key," but it often will be necessary 

 to have series of specimens, since individual variation is so 

 great that a single specimen may not show the normal charac- 

 ters and may be referred to the wrong section. Thus, a speci- 

 men of T. s. concinnus having eight supralabials might be re- 

 ferred to T. eques, or one of T. o. atratus with seven labials 

 might cause confusion, whereas a series of three or four speci- 

 mens would immediately clear up the matter by showing these 

 counts to be abnormal ones. 



