507 



MONOGRAPH OF THE GENUS 

 NEMTINA. 



Char. Gen. Molluscum trachelipodum plerumque fluviatile. 

 Testa plerumque tenuis, subglobosa, epidermide induta; dorso 

 rotundato ; ventre- subplanulato ; apertura semicirculari ; labio in- 

 terno ad marginem plerumque dentato, labio externo intus lsevi- 

 gato. Operculum semicirculare testaceum, unidentatum, nucleo 

 subterminali. 



A genus of spiral univalves, almost always found in fresb water, 

 and covered with an epidermis ; of a globose form, with a half- 

 circular aperture, the inner edge of which is nearly straight. The 

 inner lip is broad, and generally flat ; the outer Hp is always 

 smooth. The operculum is semicircular, testaceous, with the 

 nucleus near the lower end, and a tooth at the side, which fixes 

 under the inner lip. Although the shells of this genus are nearly 

 all fresh-water, comparatively thin, covered with a thickish epi- 

 dermis, and smooth within the outer hp, while the Neritce are 

 marine, solid, with a very thin epidermis, and generally crenulated 

 within the outer lip, the separation of the two genera may, per- 

 haps, be regarded rather as one of convenience than as resting on 

 any solid grounds. It will be found that many of the following 

 species are described rather comparatively than positively : this is 

 done from a conviction of the former mode being the best for 

 facilitating their recognition. 



1. Neritina ovalis (pi. cxiii. f. 121, 122), Sowerhj, Pro. 

 Zool. Soc, 1849. 



N. testa transverse ovata, extus nigra, intus cinerea ; spira nulla, 

 apice terminah, apertura ovali magna ; labio externo confluente, 

 labio interno septiforme, complanato, aurantio, margine obscuris- 

 sime crenulato. Operculo nigro, radiato. 



More regularly oval than the other patelliform species, with the 

 apex quite terminal. Outside black, rather rough ; inside blueish, 

 excepting the columella, which is orange. It is flat, septiform, and 

 very obscurely crenulated at the edge. 



Mr. Cuming's collection. 



