266 TROPICAL MEDICINE AND HYGIENE 



large species whose bite is said to be fatal : it occurs in 

 several of the West Indian islands, and is ringed much 

 like E. surinamensis. 



American Crotalince. America is the headquarters of the 

 sub-family, all the known genera being represented there.. 



(a) Ancistrodon (see p. 259). There are three species, 

 all belonging to North or Central America, (i) Ancistrodon 

 piscivorus, the Water-Mocassin or Cotton-mouth, grows to 

 5 ft., and is found in swamps and brakes readily taking 

 to water in Eastern North America. It is distinguished 

 from other American species of the genus by the absence 

 of a loreal shield. (2) Ancistrodon contortrix, the Copper- 

 head, has much the same distribution and size as A. pisci- 

 vorus, but it has a loreal shield, and its ground-colouring is 

 yellowish or reddish-brown. The American Ancistrodons- 

 are said to be more deadly than rattlesnakes. 



(6) Lachesis (see p. 261). There are twenty-^two species,, 

 chiefly South American, and none occurring north of 

 Mexico. They are bush and forest snakes, (i) Lachesis 

 mutus, the dreaded Bushmaster, is found from Panama to 

 Bolivia and Brazil, and may attain a length of 14 ft. 8 to- 

 12 ft. being quite common. Its distinguishing marks, 

 besides size, are its narrow supra- ocular shield, and its tail, 

 which ends in a sort of horny spike covered all round with 

 small scales. It is said to be extremely fierce. (2) Lachesis 

 lanceolatus and (3) Lachesis atrox, both known as Per de 

 Lance (Labarria in British Guiana, Jararoca in Brazil), 

 have a wide range in Tropical America, the former also 

 extending to some of the West Indian islands. Both are 

 distinguished from the Bushmaster by having large supra- 

 ocular shields, and by the tail ending in the ordinary 

 way with sub-caudal shields, not scales, at its tip. The 

 Per de Lance is spoken of as a deadly snake. 



(c) Crotalus : Rattlesnakes. The Rattlesnakes are well 

 known from the loose rings of hardened epidermis at the 

 end of the tail, the vibrations of which give rise to sound. 

 The head is broad and is covered with small scales alone, 

 or with scales and small shields ; the neck is narrow, and 



