CROCODILIAN^, LIZARDS, AiND SNAKES. 1107 



The species ditfer as follows : 



I. .Superior labials eight to uiue. 



(f. Scales in 21-25 rows. 



Body slender, compressed; scales in tvr on ty-one rows; preocnlars two ; dor- 

 sal spots small, no postocular band S.aimnlatitm Liiniirus.' 



Body robust, cylindric; scales in twenty-one rows; preocnlars two; dorsal 

 spots large, wide; a conspicuous black postorhital band. 



S. yiicataiiense Cope.^ 

 Robust; scales 23-25 rows ; preocnlars tliree; conspicuous dorsal spots, and 



postorbital band S. Heptentrionale Kennicott. 



Robust; scales twcnty-oue; one preocular; numerous transverse black dor- 

 sal rhombs, and no lateral spots; top and sides of head black. 



S. 2)er.sonatum Cope.' 



Robust; scales twenty-five; loreal longer than deep; brown with yellow 



crossbars and black-edged brown dorsal rhombs ..S. rhomhiferum Giinther.^ 



Robust; scales twenty-three; preocuhus two; loreal square; black with 



narrow gray cross bands; a conspicuous postocular band; labials nine. 



S.fnnatum Cope.'' 

 a a. Scales in nineteen rows. 



Robust; preocnlars two; loreal short; parietal quite or nearly touching 

 postocular; cross bands much wider than interspaces; a postocular stripe. 



.S. nu/rofaseiatiim Giinther. 



II. Superior labials seven. 



Robust; scales nineteen rows; preocnlars two; pale brown, with several 

 rows of small blackish spots; a blackish half collar above ; head paler; 

 no postocular band S. pacijicum Cope. 



SIBON SEPTENTRIONALE Kennicott. 



Sihon septentriouaUfi C(M«e, Proc. V. S. Nat. Mus., 1892, p. 678. 



IHpsaa septenlrionalis Kennicott, U. S. Mex. Bound. Surv., Reptiles by Baird, II, 



p. 16, pi. 8, fig. 1. 

 Sibon annulatum septentrionale Cope, Check-list N. Amer. Batr. Rept., 1875, p. 38; 



Cat. Batr. Rept. Centr. Amer. Mex., 1887, p 67. 

 Leptodira septentrionalis Boulenger, Cat. Snakes Brit. Mus., Ill, 1896, p. 93. 



Body moderately slender, very much tapering anteriorly and poste- 

 riorly. Tail slender, about one-hfth the total length. Head ovoid, 

 somewhat depressed, very large, twice as wide posteriorly as the neck. 

 Crown flattened, concave behind the eyes; temporal regions much 

 swollen. Snout obtusely pointed, scarcely more depressed than the 

 vertical region. Vertical plate pentagonal elongated, broader in front, 

 concave on the sides. Occipitals triangular, nearly as broad as long. 

 Superciliaries small. Kostral broader than high. Nasals much larger 

 than prefontals, two-thirds as high as long, emarginate above to receive 

 the exterior edge of prefontals. Loreal smaller than upper preorbitals, 



' Leptodira annulata GnnihQV, Dipsas anntilala Dumoril and Bibron ; South America, 

 Panama, Costa Rica. 



- Sihon annuJatum ijucatanense Cope Proc. Acad. Nat. Sci. Pliila., 186ti. p. 127; Yuca- 

 tan, Belize. 



■^ Leptodira personata Cope, Pro<'. Acad. Nat. Sci. Phila., 1868, p. 310; Mazallan, 

 Mexico. 



^ Leptodira rhomhifira (Jiinther, Ann. Mag. Nat. Ilist., 1872, ]t. 32. 



■' Sibon frenatum, Proc. U. S. Nat. Mus., 1886, p. 181; Jalapa, Mexico. 



