INTRODUCTION. XXI 



put themselves in the attitude of defense, and resent attack when unable 

 to escape; their bites are mere scratches, and sin add occasion no anxiety. 



Although typical earth, water, or tree snakes are very distinct, the 

 intermediates are so numerous as to make it impossible to classify them 

 according to habits. It is well, however, to note the differences of the 

 types, without losing sight of the fact that there are forms of such struc- 

 ture and habits as to make their position doubtful in either of the three 

 divisions. 



Ground Snakes are rather stout and thick in body and tail. Their bodies 

 are usually cylindrical, and the tails most often short and conical. For the 

 most part they have smooth scales. The eye is of moderate size to small, 

 and the pupil generally round. Certain species which burrow, as those of 

 Heterodon, have valvular nostrils, and rostrals shaped somewhat like shovels 

 or plows. 



Wafer Snake* are well represented in the genus Nerodia, in which 

 the body is stout and fusiform, the tail tapering, the nostrils valvular and 

 near the top of the snout, and the scales keeled. One of the most peculiar 

 forms of the division is Herpeton, which has a pair of feelers or tentacles 

 extending forward from the muzzle. 



Tree Snakes are very long and slender. Their eyes are comparatively 

 large, and the pupil is either round or oblong, erect or horizontal. Tactile 

 appendages to the snout are possessed by some species. In general they 

 feed upon the small animals that make their homes among the leaves and 

 branches. Bachiodon, an African genus, feeds on eggs; it has very weak 

 teeth in the jaws, but the inferior processes of the vertebrae of the neck 

 extend into the sesophagus, and are tipped with enamel for the purpose 

 of crushing the shells after so far swallowed that the contents may not 

 escape by the mouth and be wasted. Green is a very common color in 

 this division. 



In the list of families in this suborder north of Tehuantcpec, several 

 really belong to South America, being introduced on account of straggling 

 species reported from the Mexican region. Of the Dipsadince, a single 

 species ranges north of Mexico into Arizona and Texas. From Southern 

 Mexico two species of Scytalince have been noted. There are two species 

 of Dmdrophince, which also range into Mexico. The most abundant North 

 American snakes belong to the Niatricince, of which species, as Eutcenia 

 sirtalis, range over the whole continent, excepting the far North. The 



