350 Catalogue of Terrestrial and [June, 



IV. — Descriptive Catalogue of Terrestrial and Fluviatile Testacea, 

 chiefly from the North-East Frontier of Bengal. By W. H. Benson, 

 Esq. B. C. S. 



The species of land and fresh-water shells described in the following 

 pages, form a collection, chiefly made in the hills on the N. E. frontier, 

 which was purchased by the Asiatic Society of Bengal in 1833. One 

 of the land shells, Scarabus triangularis, and two Neritince and a 

 Melania among the fluviatile shells, inhabit the jungles and streams 

 of the Gangetic Delta, and were probably collected on the route to 

 Sylhet. Several shells belonging to the genera Cerithium, Cancellaria, 

 Planaxis, Phasianella, and Pedipes, which occur in the collection, have 

 been omitted, as being, in all probability, marine, or semi-marine 

 productions procured from the embouchures of the Deltaic rivers. 



1. Vitrina Gigas. Testa tenui, corneo-virente, ovato-depressa, 

 auriformi, velociter crescente, supra planata, rugis concentricis et 

 striis radiatis decussata ; subtus tumida ; ultimo anfractu valde ventri- 

 coso, pene totam testam eflbrmante ; apertura transversa, rotundato 

 ovata, prsegrandi ; labio valde arcuato. Diam. 1.15 poll. 



This shell is so flattened, and enlarges so quickly, that it has very 

 much of the appearance of one of the macrostomata, to which I refer- 

 red a specimen from the caves of Sylhet, recently fossilized with calc- 

 tuff, when I first saw it. It has only two whorls exclusive of the 

 apex, and differs in size, in the depression of the spire, in the very 

 arcuated left lip, and the more extended mouth from the European 

 species V. elongata. I believe that it is the first shell truly belong- 

 ing to this genus which has been ascertained to inhabit India. Since 

 I became acquainted with it, I have met with a second species alive, 

 adhering to dead leaves at the roots, and to the lower part of the 

 trunks of trees in the teak- wood attached to the Botanic Garden of 

 Calcutta ; but the characters of the animal restrict it to the genus 

 Helicarion of Cuvier. Whether V. Gigas belongs to Cuvier's Heli- 

 colimax or to Helicarion, cannot be ascertained without an examination 

 of the animal ; I therefore leave it in the original genus as defined 

 by Lamarck. 



2. Nanina decussata. Testa cornea, discordea, sub-depressa, umbi- 

 licata ; spira exsertiuscula, obtusa ; anfractibus septem supra planatis, 

 ultimo obtuse angulato ; epidermide supra argute decussata, infra 

 radiatim striata; apertura transversa, lunata. Diam. 1 poll; axis 0.35 



On a cursory inspection of this shell, I erroneously considered it 

 to be a variety of the species " vitrinoides" Deshayes, belonging to 

 Mr. Gray's genus Nanina, (Zool. Proceedings, 8th July, 1834,) which 

 I indicated under the name of Macrochlamys in the first No. of the Jour- 



