NATURAL SCIENCES OF PHILADELPHIA. 309 



II. Nasal plates distinct; muzzle with small plates or numerous scales above. 



a. Muzzle with two marginal shields above each cantbus rostralis. 



p. An elevated narrow cuneiform rostral. 



y. The rattle acuminate. 



C. polysticta Cope. Scales 27 rows ; sup. labials 14; separated from orbit 

 by two rows. Gray-brown, with seven longitudinal rows of brown spots; top 

 of head variegated. Mexico. 



C. triseriata Wagler. Scales twenty-three rows ; two pairs of large scales 

 on top of muzzle ; six rows between orbits. Yellowish, with a dorsal series 

 of sub-round brown spots. Mexico. 



C. confluenta Say. Scales 25-7 ? (-9) rows ; labials 15 to 18, separated 

 from orbit by four rows ; six to ten rows between superciliaries Yellow line 

 from supercilium above angle of mouth ; a medial dorsal row of brown spots 

 emarginate before and behind, with two alternating lateral series. Central 

 and south-west North America. 



yy. The rattle parallelogrammic. 

 C. lucifer Bd. Gird. Scales 25-7, labials 15-16, with four rows above them. 

 Numerous sub-round blackish dorsal spots, separated by narrow yellow lines : 

 a light band from supercilia above angle of mouth. Pacific region North 

 America and Arizona. 



C. scutulata Kennicott. Scales 25 rows, superior labials 16 ; three or four 

 rows interorbital scales, bounded in front by two shields. Yellow stripe from 

 eyebrow above rictus oris ; yellowish-brown, with a dorsal series of truncate 

 brown yellow-edged rhombs ; tail black-ringed. Arizona. 



C. atrox Bd., Gird. Scales 25-7 rows, labials 15; muzzle with small 

 scales above; yellowish, with a dorsal series of complete yellow-edged brown 

 rhombs ; yellow band from supercilium above angle of mouth. Texas and 

 Sonora. Tail black-ringed. 



C. adamaxtea Beauvois. Scales 27 rows; labials 15 16; muzzle above 

 with small scales, acuminate. Brown, with three series of brown yellow- 

 edged complete rhombs, tbe median larger, only separated by tbeir yellow 

 margins ; a yellow line from supercilium to angle mouth. Florida and 

 Georgia. 



C. horrida Linnaeus. Scales 23 5 rows, all carinate ; labials 12 14 ; two 

 rows between them and orbit. Light line from superciliary plate to angle of 

 mouth ; two series of dorsal rhombs, confluent except on the anterior part of 

 the body, forming transverse zigzag blotches ; tail black. Eastern district 

 of North America. 



/?/S. An equilateral broad or depressed rostral. Rattle acuminate. 

 C. enyo Cope. Scales 23 rows, sup. labials 13; superciliaries separated by 

 six rows ; scales on muzzle small. Above yellow, with a median series of 

 small transverse rhombs, which are prolonged into vertical lateral black 

 bars; former median and longitudinal on neck; light line to above canthus 

 oris. Lower California. 



C. Tigris Kennicott. Scales 21 3 rows, numerous smooth plates on top of 

 muzzle ; labials 14, separated by two rows from orbit, superciliary space wide. 

 Yellowish ash, with small doral blotches on anterior one, and cross-bands on 

 posterior two-thirds of body. Deserts of Gila and Colorado. 



an. Upper margin of canthus rostralis with small scales like the others. 

 c. Prenasal in contact with rostral; superciliary prolonged into a horn. 



C. cerastes Hallowell. Two elongate preorbitals ; rostral broad as high ; 

 rattle parallelogrammic. Scales 21 3; labials 11 13. Light yellowish, 

 1866.] 



