CROrODTLTANS, LIZARDS, AND SNAKER. 339 



For farther observations, see chapter on " Geographical distribution." 

 Tlie North American species may be compared in greater detail as 

 follows : 



A. Cephalic plates perfectly smooth. Supraorbital regiou Avith one erescentic series 

 of very large plates, bordered externally and internally by a series of small 

 ones, making three in all. Two verticals. 

 Scah^s largo, those on side of neck very spinons. Color grayish, without con- 

 tinuous cervical collar; back with median transverse bands. 

 a. Inner row of supraorbital scales wanting behind. 

 Color yellowish green. A black collar around neck, interrupted above. Dorsal 

 dusky bars, with a tendency to two series of blotches behind. 

 Scales of back in thirty-two series. Scales strongly carinated, pointed, and 



mucronate S. clarkii. 



Eighteen and twenty rows of scales between rump and nape ; parietals wider 

 than interparietal, which is not wider than long; lateral scales larger than 

 abdominal. Yellow, with a wide I'ed-orango band on each side, sometimes 

 covering the entire back, the middle of which is marked by indistinct 



brown crossbiirs sometimes wanting; large S. zosteromus. 



aa. Inner orbital marginal plates continuous. 

 Dorsal scales in thirty-three rows. Scales on inside of tibia carinated. Femoral 

 pores 13. Free portion of hind toe shorter than cephalic plates. 

 Color above greenish yellow, with two broad yellow stripes, five rows apart, 

 liack with distinct transverse blackish bars. No blue on chin in males and 



but little on the side of belly S. spinosus. 



Dorsal scales in fort}- rows, well keeled and mucronate; interparietal wide 

 as long; four preauricular free scales. 

 A pale band on each side connected by undulating black crossbands. 



S. Iristichus. 

 \\. Cephalic plates smootli. Supraorbitals in one large series of transverse plates, 

 with one internal and two external of smaller ones equal in size, making 

 four. Two verticals. No collar. 

 Free portion of bind toe shorter tliau cephalic plates. Dorsal scales about 

 equal to lateral ; strongly carinated, spinous and denticulate. Uelly scales 

 notched. About forty-one series of scales from head to tail. 

 Al)ove yellow olive, with two lateral stripes on each side, the upjier pair sepa- 

 rated by eight rows of scales; a broad stripe along middle of back. A 



series ofoblicjue dark lines above S. consohrinus. 



Free portion of hind too equal to cephalic plates. Edge of dorsal scales rounded ; 

 scarcely mucronate or denticulated. Belly scales even. Dorsal scales in 50 

 obli(}ue series. Dorsal scales larger than lateral. 

 Above olivaceous gray, with two dorsal series of rounded blotches. No cer- 

 vical collar S.Useriaiua. 



Dorsal scales mucronate, in II rows from occiput to tail, about equal to lateral 

 and ventral scales. 

 Creen, with a row of dark erescentic blotches on each side, the green some- 

 times restricted to bright spots on each side of the back .*?. u. hiseriatux. 



C. Cephalic plates smooth. Two central series of subhexagonal supraorbital plates 

 in series; the inner or larger twice as wide as the other, which is straigliter, 

 and embracing it in its concavity. There is, besides, an internal and gener- 

 ally two external series of very small plates, making five; the latter some- 

 times much confused. 

 A light line from the back nearly i)crpondicular to the shoulders witli a black 

 one .interior to it, sonietimes extended into a collar encircling the back of the 

 neck. No longitudinal dark line from shoulder to head. 

 a. A distinct, black collar complete above. 



