stripe which continues onto tlie iieclc. White or light 

 yellowish below. 



Distribution: Rain forest and tropifal deciduous 

 forest regions from southern Nicaragua to the coastal 



Mexico and Central America 



Mexican Pigmy Rattlesnake, Sistrurus ravus 

 (Cope). 



Identification: A small brownish rattlesnake with the 

 9 usual i)lates on the crown ; the only such rattle- 

 snake within its range. Body moderately stout ; head 

 oval. Adults average about 20 inches in length ; a 

 large individual is 24 inches. 



Ground color brown or gray witli 2.j-3."i small ir- 

 regular blotches down the back, small lateral spots 

 may fuse with the dorsal row to form irregular cross- 

 liands; 6-8 dark bands on tail. Head unicolor brown 

 or with an arrow-shaped median dark marking. 

 Ventral surface yellowish, blotched with brown. 



Dor.sals moderately keeled, in 21-23 rows at midbody, 

 fewer posteriorly. Ventrals 1.3H-1.")2; subcaudals 20-30. 



Distril/iitinn: Tin- southern part of tlie Mexiian pla- 

 teau. 



Il(inuil:s: This is a small species and is not con- 

 sidered dangerous. 



Figure 33. — Bushmaster, Lavhesis niiitKs. I'lioto by 

 Isabelle Hunt Conaiit. 



Inwhuuls of Ecuador and the Amazon basin of I'eru, 

 H<iliviM, Brazil, and Paraguay. 



Reuiarl;'<: This is potentially a very dangerous 

 snake with long fangs and large amounts of rather 

 to.xic venom. However, its strictly nocturnal habits 

 keep it from coming into contact with humans ex'cept 

 rarely and few bites have been recorded. 



Specific antivenin is produced by the Instituto Bu- 

 taiitau (Brazil). 



CROTALIDAE: Genus Sistrurus Gorman, 1883. 

 I'io'iiiy Rattlesiiukes, 



Three species are recognized: two are in the eastern 

 and central I'nited States, the other in the southern part 

 of the Mexican plateau. None is considered especially 

 dangerous, although N. catcnutiiii is reported to some- 

 times cause death in children. 



Definition: Head broad, very distinct from narrow 

 neck : canthus obtuse to acute. Body cylindrical, ta- 

 pered, slender to moderately stout ; tail short, terminat- 

 ing in a relatively small horny, segmented rattle. 



Eyes small to moderate in size; pupils vertically el- 

 liptii-al. 



Head scales : The 9 typical scales on the crown. 

 Laterally, nasal in contact with upjier preocular or seiia- 

 rated from it by loreal scale; eye separated from 

 supralabials by 1-3 rows of small scales. 



Body scales: Dor.sals strongly keeled, with apical 

 pits, In 19-27 nonoblicjue rows at midbody, fewer an- 

 teriorly and posteriorly. Ventrals 122-lGO ; subcaudals 

 llt-39, all entire or a few posterior ones paired. 



Iiiinnrls: Brattstrom (19G4) suggested that the 

 genus Kistnirns was not recognizable, and that the 

 three iiKluded species should be placed with the other 

 ratlesnakes in the genus Crotaliis. 



FiGURK .34. — Mexican I'igmy Ualllesiiake, Sislrurii.i ra- 

 ms. Photo by Isabelle Hunt Conant. 



REFERENCES 

 (See a/so General h'eferences) 



WXWXV.'A del TOKO, Mi«riie] 1060. Los rep- 

 tiles (le Chiapas. Inst. Zool. Estado, Tuxtla 

 (iiitieiiez, Chiapas. ATexico. 7-20-t p., illus- 

 ti-ated. 



IM'KCEU, AV. Leslie l!».-)() A Preliminary Study 

 dl' the Jiiiiipiiio; A'iper, Uothvupx numin'ifer. 

 Bnll. Chicago Acad. Sci., 9 (3) : 59-67, 1 pi. 



CLAKK. Herbert C. 1042 Venomous Snakes. 

 Some Outral .Vmerican Records. Incidence 

 of Snake-bite Accidents. Anier. Jour. Trop- 

 ical Med., 22 (1) : 37^9. 



MERTEXS, Robert. 1052. Die Amphibien und 

 Reptilien von El Salvador, aiif Griind der 

 Reisen von R. Mertens und A. Zilch. Abh. 

 Senckenbergischen Ges., 487: 1-120, 16 pis. 



57 



