1836.] in the Society's Museum. 749 



which it differs more especially in the greater proportionate size of 

 the aperture, in the perfect parallelism of the inner lip with the axis 

 of the shell, its denticulation nearly throughout its whole length, in- 

 stead of merely in the centre ; in the compression of the whorl at the 

 back of the callus, and its subcentrical position, thereby occasioning 

 the approach of the shell to a symmetrical configuration, and finally 

 in its suite of colours. It is much less frequent than N. depressa. I 

 have met with only two specimens, in the Hugli at Fort William, 

 and in Tolly's Nullah, adhering to piles and bricks. The aperture is 

 livid white, with blackish shades. The operculum, following the form 

 of the aperture, is broader than in N. depressa, and its two costate 

 teeth are more developed. 



36. Neritina tigrina. Testa globoso-conoidea, cornea vel olivacea, 

 lineis subtilissimis, fasciis angulato-flexuosis, maculisque nigris longi- 

 tudinaliter strigata ; suturis obsoletis ; anfractu ultimo ventricoso, 

 infra suturam excavato-depresso ; apertura obliqua, intiis alba ; callo 

 columellari macula lutea notato ; labio medio emarginato, infra pro- 

 jecto, emarginatione projecturaque ambabus denticulatis. 



The specimens, in the collection, of this very handsome species are 

 of an ordinary size. A fine individual which I took adhering to the 

 piles which defend Fort William from the action of the Hugh, 

 measures 1.35 inches in length. The operculum is very strong, and 

 besides the two exserted mucrones at the lower part, have two strong 

 radiating curved ribs on the inner surface, the central one of which 

 forms, at its termination, a third mucro. In addition to the living 

 examples which I met with in the River Hugli, I have a beautiful 

 specimen which I captured in the aqueduct that supplies the old 

 Course at Calcutta. When decorticated the ground of the shell is 

 white ; and the black markings assume a purplish hue. 



Two other very distinct species of Neritina with oblique apertures 

 inhabit the waters around Calcutta. I propose shortly to describe 

 them as JV. retifera and N. obtusa. 



In all the species of Neritina of which I have seen the operculum, 

 that accessory piece is smooth and polished, exhibiting only faint 

 radiating striae or striae of growth ; but in a ribbed Nerita which 

 occurs at the embouchure of the Hugli, the exterior surface of the 

 operculum is granulated like shagreen. Is this latter character per- 

 manent in the genus Nerita ? if so, it will furnish an additional mark 

 to distinguish the two genera. 



37. Navicella compressa. Testa transverse elongata, compressa, 

 lutea, albida, vel cornea, lineis munitissimis transversis diverse colo- 



5k 



