ORDER OPHIDIA. 267 



during those irregular movements which the fear of 

 its aspect causes them to make.* 



Most part of the species have scales on their 

 heads similar to those on the back. 



The species most common in the United States, 

 (Ci'otalus Horridus, L.) Catesb. II. xli. is brown, 

 with irregular blackish transverse bands. 



That of Guiana, (Crotalus Durissus,') Lacep. II. 

 xiii. 2, has lozenge-formed spots bordered with 

 black, and four black lines along the upper part of 

 the neck. Both are equally redoubtable, and can 

 cause destruction in a few minutes. They generally 

 attain to the length of six feet.t 



Some species have the head furnished with large 

 plates, t 



We should approximate to the Crotali, 



Trigonocephalus, Oppel ; Bathrops, Spix ; 

 CoPHiAS, Merrem ; 



Which are distinguished by the absence of the noisy 

 apparatus, but have the same fbssets behind the 

 nostrils, and are at least equal to the crotali in the 

 violence of their poison. 



* See Barton, " A Memoir on the Faculty of Fascinatioji attributed to 

 the Rattle-Snaked Philad. 1 796. 



t These two names of durissiis and horridus have been variously ex- 

 changed between the two species by naturalists. 



X It is of this subdivision that Mr. Gray has made his genus Crotalo- 

 PHORL'S, and Mr. Fitzinger his genus Cauuisona. The Crotalus Milians, 

 L. Catesb. II. 42, appertains to it. 



