THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 42. JUNE 1861. 



XLVIII. — On the Ophidian genus Helicops. 

 By Dr. Albert Gunther. 



The genus Helicops, as defined by Dunieril and Bibron, is a 

 very natural group of Snakes ; it comprises those freshwater 

 snakes from Tropical America which have the scales keeled, the 

 anterior frontals united into a single triangular shield, and the 

 posterior maxillary tooth longest, smooth, and at some distance 

 from the others. At the time of the publication of the Catalogue 

 of Hydroid Snakes, Dr. Gray was only acquainted with two 

 species, which he referred to two genera, Uranops and Helicops, 

 the former being distinguished by very strongly-keeled scales, 

 the latter by having the scales smooth on the anterior part of 

 the body. Since that time, a third species {H. Leprieurii) has 

 been discovered, intermediate between those extreme forms, and 

 proving their close affinity. This is confirmed by numerous 

 examples since procured by Dr. Gray for the British Museum; 

 and among these there are two other species which have not yet 

 been described : — 



1. Helicops modestus. 



Dirignosis. — Three pairs of chin-shields ; occipitals narrow, elon- 

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

 on the anterior parts of the back with feeble keels. Blackish 

 above, with two indistinct darker longitudinal bands ; lower 

 parts uniform dull yellowish. 



Hab. Tropical America? 



Description. — Head depressed, triangular, not very distinct 



from neck ; rostral shield ])eiitagonal, much broader than high ; 



anterior frontal single, triangular, with the posterior side longest ; 



one pair of posterior frontals, each being not much larger than 



Ann. ^ Mag. N. Hist. Scr. 8. Vol \'\u 28 



