12 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



The ventral surface is ordinarily some shade of slate, often slightly 

 iridescent, and frequently marked with red or black. The bases of the 

 abdominal scutes nearly always possess a varying amount of black 

 which is concealed by the overlying edge of the preceding scute. 

 Where this pigment is well developed it forms a black bar along the 

 base of each ventral scute, which is enlarged at either end into a 

 spot that jirotrudes beyond the edge of the superincumbent scute, 

 thus giving rise to the appearance of a row of spots along the sides of 

 the belly. In some forms this bar is enlarged in the middle, and 

 frequently to such an extent that it projects beyond the overlying 

 scute and forms a median ventral band that varies in width from a 

 narrow line to a broad band that covers most of the belly (elegans, 

 melanogaster) . The ground color of the belly blends with the color 

 of the dorsal surface on the first row of scales. 



The area inhabited by the genus Tliamno'phis, as at present known, 

 includes all of North and Middle America north of the southern 

 boundary of Guatemala and south of the fifty-second parallel of 

 north latitude, although it is possible and even probable that both of 

 these limits are surpassed. These snakes are known from almost 

 every part of the intervening country except the lower part of the 

 peninsula of Lower California "^ and the State of Sonora, Mexico, but 

 the absence of records from both of these localities is probably due 

 to the fact that these regions have been but little explored. The 

 distribution of the different forms will be considered in detail when 

 these are taken up. 



HABITS AND HABITAT RELATIONS. 



As in the case of most reptiles, very little is known of the habitat 

 relations of the garter-snakes. Where detailed notes are available 

 they will be given in the discussion of the different forms. In general 

 it may be said that while the snakes of this group are not aquatic 

 they apparently ])refer the vicinity of water, as they occur in such 

 places much more abundantly than elsewhere, although they are 

 found not uncommonly on higher ground and in dryer situations. 

 The extent to which they prefer damp situations also varies some- 

 what with the form and the region, as will be shown later. 



Their food is in conformity with the nature of their habitat, and 

 varies accordingly. Thus, individuals in the vicinity of water appar- 

 ently subsist largely on frogs, tadpoles, and fish, while on the dryer 

 uplands they have been observed to eat insects, earthworms, toads, 



o A single specimen has been recorded from Cape San Lucas, Lower California, but 

 there is good reason to believe that there is an error in this record. (See p. 161.) 



