SERPENTS OF NORTHEASTERN UNITED STATES 365'- 



CROTALIDAE 

 B. Deep pit between eye and nostril; upper jaw with erectile poison fangs; form 

 stout; bead more or less triangular; neck constricted; subcaudals entire 



a Tail without rattle A n c i s tr o d o n (p. 385)' 



b Tail with small rattle; top of bead covered with 



plates......... Sistru rus (p. 386) 



c Tail with larger rattle; top of head covered with small 



scales C r o t a 1 u s (p. 387) 



Color key to species 



The author has prepared a purely artificial key, based almost 

 entirely on color and pattern, which is here appended. As it does, 

 not require handling of the specimen, it furnishes a convenient 

 means of identifying live specimens whose specific character is in 

 doubt. The numbers at the right refer to the similarly numbered 

 specific descriptions which begin on p. 366 of this bulletin. 



Owing to the great variation in color and pattern sometimes 

 shown by individual specimens, identifications made by means of an y 

 key based purely on these characters must not be accepted as deci- 

 sive, but should be verified by reading over the characters given in 

 the specific descriptions, under the head of that species to which the 

 key seems to point ; and by careful comparison of the specimen, 

 with the figure given for each species. 



a Color of back uniform; no marked spots, blotches or stripes 



Color green; scales smooth 4 



Scales rough , 5 



Color black; no lighter markings 6 



Some scales white-edged , . . . 8 



Conspicuous yellowish neck ring 2 



Color reddish brown; below pink; head not distinct from body 1 



Color chestnut brown; below pink; head distinct from body 17 



Below grayish 16 



b Striped longitudinally; with or without additional spots 



Striped black and brown; no spots 14 



Brown and yellow; no spots; abdomen unicolor; very slender . . 18 

 Olivaceous and yellow or brown; dark spots on back and sides 



in several rows 20 



Greenish brown and brown; below reddish yellow, with dark 



spots 13 



c Spotted, blotched or transversely banded above 



1) No rattle; head tapering into neck and body, not triangular 



