426 Dr. A. Giinther on the Ophidian Genus Helicops. 



the prefrontal; vertical elongate, with the lateral margins 

 slightly convergent anteriorly ; occipitals elongate^ thrice as long 

 as broad. The nostril is on the upper side of the head, small, 

 at the end of a groove which incompletely divides a quadran- 

 gular shield into an anterior and posterior portion. Loreal 

 shield large, covering the central part of the antorbital ; the 

 upper and lower ends of the ant- 

 orbital are broader than the middle, 

 which is overlapped by the loreal. 

 Two posterior oculars, in contact 

 with a large temporal shield, which 

 has a small shield beneath ; the 

 other temporal shields are scale-like, 

 except one on the side of the extre- 

 mity of the occipital, which is larger 

 than the rest. Eight upper labial 

 shields, the eye being above the 



fourth ; the third enters the orbit Helicons modestus. 



only with a point. The first pair of 



lower labials form a suture together behind the central labial; 

 and there are three other pairs of chin-shields besides, the middle 

 one being the smallest. The scales on the sides are smooth, 

 those along the middle of the back provided with feeble keels, 

 the keels becoming stronger on the posterior parts of the body. 

 Ventral shields 125; anal l/l; subcaudals 43. 



The posterior maxillary tooth is somewhat distant from, but 

 not much longer than, the rest. 



The dark longitudinal bands are very indistinct, and run along 

 the sides of the back. 



Length of the cleft of the mouth §rds of an inch, of trunk 

 16 inches, of tail 4 inches. 



The specimen on which I have founded this species was pro- 

 cured from the Leyden Museum, and was marked as coming 

 from North America. It is, however, very doubtful whether 

 species of this genus go so far northwards, and it is probable 

 that this very distinct species comes from Tropical America as 

 well as its congeners. 



2. Helicops pohjlepis. 



Diagnosis. — Two pairs of chin-shields ; occipitals rounded, as 

 long as the vertical. Scales in twenty-six rows, strongly 

 keeled. Brown above, with three series of indistinct dark 

 spots ; the black colour is predominant on the lower parts, 

 and nearly entirely suppresses the whitish ground-colour. 



Hab. Upper Amazon. 



Description, — Head broad, obtuse, short, not very distinct from 



