226 DR. H. GADow ON MEXICAN [June 6, 



ViPERiDiE. — CuoTALiNiE, taken together, occur all over Mexico, as 

 is to be expected of a group which ranges from Massachusetts and 

 Bi-itish Columbia to Argentina, but they fall into two lots : — 



I. Northerners, with their archaic centre in Sonoraland. 

 Ancistrodon is chiefly Nearctic ; but of the terrestrial forms 

 A. hilineatids extends along the Pacific side of Mexico, including 

 Tres Marias Islands, to Yucatan and Guatemala. Of Sistrurtis, east 

 of the Rocky Mountains, S. ravus has been described by Cope 

 from Vera Oruz. Crotalus, the main genus, radiates out from the 

 tablelands of Arizona ; G. terrifi,cios (Jiorridus of some authors) is 

 the only species which extends right through Mexico to the 

 Isthmus, and thence right into Argentina, avoiding, however, the 

 moist and wooded Tierra Caliente. It is the only Rattlesnake in 

 South America. C. triseriatus is confined to Mexico's mountains, 

 I'anging from the ISTevadp de Colima right across to Citlaltepetl, 

 where I have found it at an altitude of 12,500 feet. 



II. Southerners. — Lachesis, an essentially Neotropical genus, 

 a few species of which extend into the Eastern and Western 

 States below the plateau. L. lanshergi has the widest distribution, 

 and it is the only Pit-viper which has entered the Lesser Antilles, 

 the larger and older islands being free from poisonous snakes. 



The Rattlers, or " Yiboras de cascabel," are not much feared, 

 being " manzitos " (rather tame), meaning sluggish and not 

 inclined to strike unless provoked ; moreover, they always try to 

 give fair warning with the rattle, which they sound only when 

 coiled up and prepai'ed to strike, but not when crawling away as 

 they generally attempt doing. The Lachesis lanceolatus, the " Per 

 de lance " of Martinique, &c., " Rabo de hueso " or Bone-tail of the 

 Mexicans, on account of the curiously coloured and spike-like tip 

 of the tail, behaves quite differently. It is very cjuick, highly 

 irascible, and even known to make for its pursuer, therefore much 

 dreaded. In fact the few cases of snake-bite which I could 

 ascertain, mostly fatal, were due to this species. 



Resume of the Distribution of Ophidia, 



Typhlojyidce. — Central and South American, Atlantic Mexican 

 and Antillean *. 



Glauconiidce. — Remnants of Sonoranto Neotropical distribution ; 

 they may reasonably be expected to be foiind in the Antilles. 



Boidce. 



1. Xerophile Sonoran, not Antillean. 



2. Hygrophile Central South American, Mexican Tierra 



Caliente, and Antillean. 



* Tor the present purpose only those Snakes are considered Antillean which occur 

 in the Greater Antilles. The Lesser Antilles, entirely volcanic and of much younger 

 date, have received the Lachesis, Oxyrhopus, and Glaucoma directly from the opposite 

 part of Venezuela. 



