96 BULLETIN 199, UNITED STATES NATIONAL MUSEUM 



8. Usually less than 12 femoral-preanal pores, the pore scales usually separated 



by 1 or more intervening scales 9 



Pore series 17-23, the pores surrounded by several small scales and usually 

 contiguous; temporal and occipital horns very elongate; 2 series of lateral 

 fringes on abdomen; an indistinctly enlarged series of longitudinal gular 

 scales on each side of chin, more evident posteriorly; a dark dorsal streak; 

 immaculate white on venter; tail much flattened; occasionally traces of 

 abdominal keeling present m'callii (p. 99) 



9. Pore series about 8 on each side; 3 enlarged temporals and 2 enlarged occipital 



spines, tending to curve laterally somewhat; small species, 72 mm. snout to 



vent; venter immaculate white platyrhinos goodei (p. 102) 



Pore series 7-12, the temporal and occipital horn much reduced; superciliary 

 spine short but heavy and prominent; a single series of scales in lateral 

 fringe; venter usually punctate with dark; only rarely is the tympanum 

 visible platyrhinos platyrhinos (p. 101) 



10. Four much-elongated, flattened occipital horns, contiguous with a like tem- 



poral series, all directed more or less in same general plane; breast scales 

 keeled; 1 distinct lateral fringe and a small secondary fringe indicated. 



solare (p. 104) 



Never more than two strongly developed occipital horns (occasionally a very 



small median single scale may be present) 11 



11. Occipital horns at least twice as long as basal width; chin shields forming 



serrate series strongly visible from dorsal view of head; gulars with serrate 



series of enlarged scales coronatum group 17 



Occipital horns not twice as long as basal width; no serrate chin shields or 

 specialized serrate series in gulars 12 



12. Head not strongly notched or emarginate between occipital horns, distance 



between bases of horns one-half to rarely one and one-half times basal 

 width of horn; occipital horns distinctly larger than superciliary horns. 



orbiculare group 14 

 Head strongly notched or emarginate between occipital horns; horns very 

 short, their bases separated by a distance equal to 2 to 3)4 times basal width 

 of a horn; occipital and superciliary horns subequal in size. 



douglassii group 13 



13. Tail length a little less than half snout-to-vent length but distinctly longer 



than width of head; gular scales not convex; chest scales smooth. 



douglassii hemandesi (p. 100) 



Tail very short, very slender, length less than width of head; gular scales 



convex, and chest scales keeled douglassii brachycercum (p. 100) 



14. Occipital spines nearly erect, while temporal spines approach the horizontal, 



all relatively long; top of head conspicuously concave, superciliary region 



elevated boucardi (p. 98) 



Occipital spines on same plane as temporals, approaching horizontal, all 

 shorter; top of head flat 15 



15. Temporal horns not or barely extending backward as far as posterior tip of 



occipital horns 16 



Temporal horns extending backward farther than occipital horns. 



orbiculare cortezii (p. 98) 



16. Occipital horns extending posteriorly farther than posterior temporals; pre- 



anal area with preanal pores not confined to a single row (usually several 

 irregularly placed pores or 2 longitudinal rows of 2 to 4 scales) . 



orbiculare orbiculare (p. 97) 



