SYNOrSES AND DESCRIPTIONS. 15 



about one third as large as the prefrontals. Rostral subtriangular, broader 

 than high. Nasal divided, nostril mainly in anterior portion. Loreal 

 small. Preocular narrow, high. Postoculars two (sometimes one), small, 

 lower resting on the fifth labial. Labials eight, fourth and fifth in orbit, 

 sixth and seventh larger. Infralabials nine, sixth larger. Submentals 

 two pairs, anterior larger, posterior separated by small scales. Scales 

 lozenge-shaped, smooth, in 17 rows, medial and outer broader. Ventrals 

 244 (228—259). Anal bifid. Subcaudals 134 pairs (134—174.) 



Light greyish-brown, scales more or less punctulate with brown. Ante- 

 riorly with dark-edged transverse blotches of brcwn; posteriorly these 

 become smaller, do not descend on the flank, and are very irregular and 

 broken. Hinder portion of body with spots irregularly distributed on the 

 lower portions of the flanks. Specimen described from Acapulco, Mex. 

 Total length 33 inches ; tail 10 in. Hab. Mexico to Brazil. 



DlPSAS LEUCOMELAS. 



Himantodes leucomelas Cope, 1861, Proc. Ac. N. Sc. Phil., 296. 



Lateral borders of frontal nearly parallel, longer than the anterior. 

 Loreal higher than long. Two preoculars, not in contact with the frontal. 

 Infralabials ten, sixth largest. Scales smooth, in 17 rows, vertebral larger, 

 broader than long. Total length about three and one half times that of 

 the tail. 



Greyish, crossed by about twenty-nine black bands, which encroach on 

 the ends of the ventrals. About eighteen spots on the tail. Spotted or 

 clotted with black on the belly. A pair of black spots from the supracil- 

 iaries over the occipitals to the neck. A band of black across the pre- 

 frontals. Scale pores single. (Unknown to me.) Vera Cruz. 



Sibon. 



Fitzinger, 1826. 



Moderately long, slightly compressed, tapering to head and tip of tail ; 

 head distinct, large, broad, depressed, with broad muzzle ; tail moderate. 

 Eye medium, pupil oblong, erect. Posterior maxillary teeth longer, 

 grooved. Head-shields regular. Nasal in two parts, nostril between. 

 One or more loreals. Oculars 1 to 3 — 2 to 3, sometimes with suboculars. 

 Scales smooth, imbricate, in 19 — 23 rows, dorsal not larger. Anal and 

 subcaudals divided. Hab, Texas and Mexico to Brazil, 



