Dr. A. Gunther on the Ophidian Genus Helicops. 427 



neck ; eyes rather prouiinent ; rostral sliield penf agonal, broader 

 than high ; anterior frontal single, triangular, with the posterior 

 side rather longer than the anterior ones ; one pair of posterior 

 frontals, each being not much larger than the prefrontal ; ver- 

 tical elongate, with the lateral margins slightly convex ; occipi- 

 tals short, obtuse, and rounded posteriorly, nearly as long as the 

 vertical. Nostril and nasal plate as in H. modestus; one loreal, 

 one anterior and two posterior oculars, the latter being in con- 

 tact with a temporal shield; the other temporals scale-like. 

 Eight upper labial shields, the eye being above the fourth. There 

 arc only two pairs of chin-shields behind the anterior pair of 

 lower labials. Venti'al shields 1 33 ; anal 1/1 ; subcaudals 82 

 (three of the anterior subcaudals are undivided). 



The posterior maxillary tooth is not grooved, distant from, and 

 longer than, the rest. 



Length of the cleft of the mouth ^ inch, of trunk 12 inches. 



As the British Museum possesses examples of all the species, 

 it will be useful to make a synoptical survey of them. 



1. Helicops carinicauda. 



Coluber carinicaudus, Neuwied, Abbild. taf. 3. 

 Helicops carinicaudus, Wagler, Ic. tab. 7- 



Scales in nineteen rows ; those on the anterior half of the body 

 smooth, on the hinder part of the back and tail keeled. Two 

 pairs of chin-shields. Belly with three longitudinal series 

 of black spots, each ventral plate having three spots. (Two 

 very young specimens in the British Museum have only two 

 series.) 



Hab. Southern parts of Brazil ; Cayenne. 



2. Helicops modestus. 



Scales in nineteen rows; those on the sides smooth, on the an- 

 terior parts of the back with feeble keels. Occipitals narrow, 

 elongate ; three pairs of chin-shields. Blackish above, with 

 two indistinct darker longitudinal bands ; lower parts uniform 

 dull yellowish. 



Hab. Tropical America? 



3. Helicops Leprieurii. 

 Helicops Leprieurii, Dum. et Bibr. vol. vii. p. 750. pi. 68. 

 .Scales in nineteen rows ; those on the sides smooth, on the an- 

 terior parts of the back with feeble keels. Occipitals narrow, 

 elongate; two pairs of chin-shields. Brownish or blackish 



28* 



