96 PROCEEDINGS OF THE ACADEMY OF [JaD., 



VIPERIDiE. 



Kexj to the Genera. 



a. — No rattle, Ancistrodon. 



b. — A rattle : 



Top of head with large plates, Sistrurus. 



Top of head with small scales, Crotalus. 



ANCISTRODON Beauvais. 



Trans. Amer. Phil. Soc, IV, 381 (1799); Agkntrodon and ToxicopJds 

 B. and G., I. c, 17-19 ; Ancistrodon Cope, I. c, 681, and Kep. Nat. 

 Mus., 131 ; Boul., I. c, III, 519. 



A pair of large erectalile, perforated poison fangs in front of 

 npperjaw; no other maxillary teeth; a pit between the eye and 

 the nostril; no rattle; top of head covered with large plates; scales 

 keeled, with pits, in 21-27 rows; anal entire; subcaudals single or 

 double, or both; size large to medium. 



Hab. — Asia, North and Central America. 



Key to the Species of the United States. 



No loreal plate; a pair of post-parietals, . . 1. A. pisevvorus. 

 A loreal plate; no post-parietals, 2. A. contortrix. 



Ancistrodon piscivorus Lac6pi5de. 



Crotahis piscivorus Lacep., Serp., II, 130 and 424 (1789); Toxicophis 

 piscivo7' us and T. pufjnax'B. and G., I. c, 19, 20 ; ^4. liisciviorus Cope, 

 I. c, 683, and Eep. Nat. Mus., 1133 ; Boul., /. c, III, 520 ; Stej., I. c, 

 406. 



Size large; body very stout; tail short, from one-seventh to 

 one-sixth of length; head broad behind, flat on top; snout 

 rounded; canthus sharp; head plates normal, but with usually a 

 pair of small additional plates behind parietals; no loreal; pre- 

 oculars 2, the upper much the largest ;. post-oculars 2, with one or 

 two suboculars; upper labials 8 (occ. 7), the third entering the 

 orbit; scales in 25 rows, strongly keeled ; ventrals 130-147; sub- 

 caudals 39-48, more or less of which are undivided, usually the 

 anterior ones. A specimen from Florida, now living in the 

 Zoological Gardens, 1,550 mm. long and 250 mm. in circum- 

 ference, is the largest I have ever seen. 



The color pattern is obscure; half -grown examples are usually 

 dark chestnut or greeni.sh olive, with blackish brown cro.ss-bands 

 Avith irregular borders. Older ones become much darker and the 

 bands are obscured; belly yellow, clouded with brown. Head 



