POISONOUS SNAKES OF NORTH AMERICA. 



423 



^oJ^rll .^^^-r-y — "" — — ^ 



Fiji- 55. 

 HEAD OF CROTALUS, FROM SIDE. 



i lufralabials ; I loreal; P lower loreal; I'' upper loreal; n^ anterior nasal; »' posterior nasal; p 

 preocular; r rostral; « supralabials; s ' 1st siipralabial; s ^ 2(1 supralabial ; .vo supraocular. 



^05^ril 



Fig. 56, HEAD OF CROTALUS MITCHELLII FROM FRONT. 



■ FRONT VIEW OF PEECEPiNG FIGURE. (See explanation of Fig. 56.) 



Synopsis of the species of Crotahis occurring in North America north of Mexico. 



«' Aiiterior iiasal iii coutact with rostral (figs. 55, 56). 

 ¥ Upper preocular uot divided vertically (figs. 55, 56). 

 c' External border of supraocular uot produced into a horn-like process (figs. 

 55,56). 

 d^ Dark spots on hack with two symmetrical light spots, one on each side of 



median line (fig. 51) C molossus. 



d^ Daik spots on hack, solid, or with only one median light spot. 



e' Dorsal pattern, consisting of dark chevron hands (fig. 52) C. horridus. 



e^ Dorsal pattern, consisting of more or less squarish spots or straight cross 

 bands (figs. 53, 54). 

 /' Rostral at least as high as wide (fig. 63). 



</' Light postsuperciliary line reaches the second scale row above com- 

 missure at least two scales anterior to angle of mouth (fig. 58). 

 h^ A well-defined vertical white line on first labial and anterior nasal, 

 occupying the posterior half of the latter (fig. 58) . . C. adamanteus, 

 h^ No white line on first labial and nasal, which are uniform in color 

 and more or less dusted over with minute blackish dots. 



t' Predominant color grayish-brown C. airox. 



i^ Predominant color reddish-brown C. atrox ruber. 



g^ Light postsuperciliary line reaches the second scale row above commis- 

 sure at corner of mouth or uot at all (figs. 59, 60). 

 A' Light postsuperciliary line one scale wide; dark postocular patch 



starts from below anterior angle of eye (fig. 59) C. confluentus. 



h- Light postsuperciliary line two scales wide; dark postocular patch 



starts from below center of eye (fig. 60) C. lucifer. 



f- Rostral wider than high (fig. 61) C. tigria. 



c- External border of supraocular produced into a horn-like process 



(fig. 66) C. cerastes. 



b- Upper preocular divided vertically (fig. 62) C. lepidus. 



a- Anterior nasal separated from rostral by scales (fig. 63). 



ft' Predominant color whitish C. viitchellii. 



b' Predominant color red C. mitcheUii pyrrhua. 



