Vol. VIII] VAN DENBURGH AND SLEVIN-GARTER-SNAKES 185 



The following facts also will be of aid in the determination 

 of specimens: 



1 Any red in the coloration indicates that the specimen be- 

 longs to one of the subspecies of T. sirtalis or to T. o. ordinoides 

 or T. o. at rains. 



2. Red on the upper surface of the head seems to be peculiar 

 to the subspecies of T. sirtalis. 



3. Red on the belly or in the dorsal line is distinctive of T. o. 

 ordinoides and T. o. atratus. 



4 The members of the sirtalis group have a much larger eye 

 and' longer posterior genials than are found in the subspecies 

 of T. ordinoides, with the possible exception of T. o. ham- 

 mondii. 



5. The members of the sirtalis group practically always have 

 19_19_17 rows of scales and a single preocular. 



6. In the subspecies of T. ordinoides 21 rows of scales are 

 almost always present, except in T. o. ordinoides and T. o. 

 atratus. 



7 Two preoculars are most frequent in T. angustirostris and 

 T. 0. hiscutatus, but are frequent in T. o. hammondii and T. o. 

 ordinoides. 



8 Absence of the dorsal stripe occurs only in four of the 

 subspecies of T. ordinoides— v'lz., hammondii, couchtt, ordi- 

 noides, and atratus,— and is usual in only hammondn and 

 couchii. 



THE SIRTALIS GROUP 



Garter-snakes of the sirtalis type have been found in nearly 

 every state of the Union. They have not definitely been shown 

 to occur in Arizona and New Mexico. Since these snakes are 

 distributed so widelv, it is to be expected that racial differences 

 may be found to distinguish the snakes of various portions of 

 this territory. This has been found true, but the geographical 

 races are surprisingly few. Of these, the best known are sir- 

 talis and parietalis, which often have been regarded as distinct 

 species Those who, with the most adequate material, have 

 studied the question, however, state emphatically that sirtahs. 



