310 Illinois State Laboratory of Natural History. 



Variety vermis. 



Black above. Two outer rows of dorsal scales and the 

 ventral surface flesh-color. Larger than var. amoenus. 



Family OROTALID^. 



With poison glands and erectile fangs, ordinary teeth few. 

 Head wide and deep, with a deep pit between the eye and nos- 

 tril. Cephalic plates crowded forward, or the frontal and two 

 parietals wanting. One or two nasals. Loreal present or ab- 

 sent. Pupils of the eye vertically elongate. Most of the dor- 

 sal scales strongly carinated. Some or all of the subcaudal 

 scutellaB united. Tail short, with or without rattle. 



This family includes the rattlesnake, water moccasin, and 

 copperhead. All are venomous, but not so dangerously so as is 

 commonly supposed. They may be known from most of the 

 non-venomous species from their stouter bodies, wider heads, 

 and the pit between the eye and nostril. No harmless snake 

 of this country has this pit. In regard to these depressions 

 Owen writes : "Secreting follicles of the skin in serpents are 

 chiefly confined to certain depressions or inverted folds of the 

 derm. These in Crotalus and Trigonocephalus constitute a pit 

 between the nostril and the eye on each side of the head." 

 A few harmless species, such as the spreading adder, resemble 

 the members of this family in stoutness of body. With the 

 exception of members of the genus Elaps, the family contains 

 the only venomous serpents in the United States. The four 

 described below are the only poisonous species which occur in 

 Illinois. 



With a rattle. Frontal and parietals lacking. Supralabials 

 separated from the eye by more than two series of small 

 plates. Most of the subcaudal scutellae entire. .Crotalus. 



With a rattle. Frontal and parietals present. Supralabials 

 separated frem the eye by two series of small plates. The 

 posterior subcaudal scutellae divided Sistrurus. 



Without a rattle. Frontal and parietals present . . Ancistrodon. 



