688 NORTH AMERICAN «NAKES — COPE. 



Some of the si)ecies grow to a very large size, particularly the G. ada- 

 manteus of North, and the 0. durlssus of South America. The former 

 is probably the larger of the two; at least we have iuformatioii of larger 

 specimens. I am credibly informed that specimens have been found 

 on the islands of the Gulf coast of Florida of 8 feet in length. Some 

 specimens of the Western subspecies G. a. atrox also reach a large size. 

 The third species in dimensions is the G. horridns, which grows on the 

 coast of North Carolina to a length of 5 feet, and proportionate thick- 

 ness. The species of the plains, G. confiuentiis, rarely reaches so large 

 a size. Its gray-greenish color readily conceals it in the sparse vege- 

 tation and it is only observed when closely approached. It is very 

 abundant uorth of the Missouri River, and extends north to the Saskat- 

 chewan, beyond the line of distribution of any other species. 



The following synopsis of the characters of the species of Crotalus is 

 the result of long familiarity with them. Some of the forms originally 

 regarded as species are treated as subspecies, owing to the evanescence 

 of their characters. In spite of the subdivision of their head plates, 

 the homologues of the plates of harmless snakes may be traced. Thus 

 there are from two to three preoculars, aud from one to four loreals. 

 The nasals are never more than two, aud the nostril is always between 

 them. There is one pair of geneials. Tlie species of section i display 

 homologues of internasal and prefrontal plates, while the same, more 

 divided, are seen in species of section ii. 



The transitional forms or subspecies in this genus, as is usually the 

 case, furnish iustructiv^e evidence as to the evolution of the characters 

 of the species. It is not improbable, as already remarked, that their 

 origin is from some genus like Lachesis, which has a scaly head aud no 

 rattle. 



I. Top ot" muzzle with three pairs of syiuuieti'ical shields in coutact. (Scales in 



tweuty-niue rows.) 



Longitudinal bauds on neck; tail uniform l)rown above; four rows of scales 

 below orbit ; yellow with black rhombs eujbraciny yellow centers. 



C. durissus. 



Longitudinal bands on neck ; four rows of scales below orbit ; blown above 

 with darker, light edged rhombs C. terriftcus. 



No longitudinal bauds on neck; tail yellow brown; large adjacent chestnut 

 red yellow-bordered dorsal rhombs, alternating with lateral chestnut 

 spots; labials fourteen ; two and three scales below eye. ..C. hasiUscus, 



No longitudinal bands on neck ; tail black ; brownish yellow above, with small 

 transverse reddish dorsal rhombs, the angles ])rodute<l as vertical 

 lateral bands ; live scales below eye C. molossus. 



II. Top of muzzle with numerous scales. 



A. Nasal plate in coutact with rostral; superciliary border not extended into a 

 process. 

 tx. Tail entirely black, 

 Kostral plate elevated; scales of canthus rostralis larger than those between 

 them ; postocular band passing above mouth angle ; iuigular spots 

 above uniting into double chevroued cross-bauds; scales twenty-live; 



C. horridus. 

 aa. Tail light, with black cross-bands. 



