Nekitinid^e.- 



-MOLLUSCA.- 



-TUREINID^. 



343 



with spiral laniinie. The axis is covered with a callous 

 deposit. The species are from the West Indies, and 

 ore pretty, smootli, and sliiniiig shells of a yellow 

 colour. They are terrestrial shells, and, like the 

 Cyclostomid;e to be afterwards mentioned, they breathe 

 free air. Thoy have no operculum, and their dentition 

 agrees with the other scutibranchiate genera. 



Family— NERITID^ = Nkuitinid^, 

 {The Nerites.) 



This family contains a number of species that are 

 either marine or fluviatile in their habits. The ani- 

 mals are destitute of the membranous fringes and ten- 

 tacular filaments which garnish the sides of the foot of 

 several of the other genera of this order. They are 

 littoral in their mode of life, being generally foimd 

 on stones and rocks along the shore, and feeding on 

 the sea-weeds that abound in such situations. They 

 appear to be more active during the night than in the 

 day. The shells are hemispherical in shape and fiat 

 beneath. The spire is lateral and very short ; the 

 inner hp is flattened, transverse, and the cavity is 

 simple, owing to the absorption of the internal portions 

 of the whirls. The aperture is semiovate, and not 

 pearly within. The operculum is peculiar in its for- 

 mation, being furnished with a process on the inner 

 side under the nucleus, which forms a kind of hinge 

 with the inner lip of the shell, — See Plate 3, fig. 2. 



Genus Nehita. — The species of tliis genus are 

 numerous, are all marine, and are chielly found in 

 warm or tropical seas. — See Plato 3, fig. 1 {Ncrita 

 undulaUi). 



Genus Neritina (^ Ncritclla). — The species 

 of this genus are fresh-water Nerites, and are found 

 in almost all parts of the world. Though inhabitants 

 of fresh water for the most part, some of the species 

 are found in brackish, and even salt water. Some of 

 them are to be met with crawling on the stones in 

 shallow water, while others are found at greater depths, 

 half buried in the mud. Some, according to Mr. 

 Adams, are amphibious, clinging to the roots of the 

 Ni|iali palms and other trees on the margins of rivers, 

 while a few inhabit the foliage of tall trees that over- 

 hang ponds and rivulets. Many of the species have 

 the apex of their shells eroded ; and Dr. Shuttleworth 

 is of ojiinion that this is caused by the animal's filing 

 otr the tips by its teeth, the marks of the teeth, he 

 says, being left on the surface of the erosion. — See 

 Plate 3, figs. .3, 4 {Neritina Oweniana and N. cariosa). 



Genus Navicella (z= Catillus). — This genus has 

 an oblong, depressed, smooth, limpet-like shell, covered 

 with a thin epidermis. The apex is small, reflexed 

 posteriorly ; the aperture is as large as the shell, and 

 has a small columellar shelf and elongated lateral mus- 

 cular scars. The operculum is very small, almost 

 rudimentary, shelly, and is applied to the dorsal surfoce 

 of the foot. — See Plate 4, fig. 1 {Terms used in Con- 

 cholofjy). The species, of which nearly twenty liave 

 been described, are usually found on the banks of rivers 

 in warm countries, as India, the Mauritius, the Philip- 

 pines, Moluccas, &c. In general they are met with 

 adhering to floating sticks, and to the petioles and 



roots of the Nipah palms and other plants that live 

 near river.s. In the island of Bourbon, the Naviedla 

 elliptica is commonly used to make a souj) for the sick. 



Family— TURBINIDiE {Top-shells). 



The Top-SiiELLS have a spiral top-shaped shell, 

 the last whirl rounded and ventricose, the aperture 

 subcircular, the inner lip smooth and simple, and the 

 interior brilliantly pearly or nacreous. The operculum 

 is subcircular, horny, with a solid, external, convex, 

 shelly coat. The species are numerous, and diversified 

 in external appearance, and the animals are all marine, 

 feeding upon sea-weeds. The Top-shells may be 

 divided into three large groups, characterized by the 

 form of the body of the animal — afiecting of course the 

 shape of the shell — and by the form of the operculum. 



Gnoup I.— TuuBiNiNA {True Top-shells). 



In this group the body of the animal is cylindrical, 

 and the shell is top-shaped, with a subcircular aper- 

 ture and operculum. 



The genus TuuBO may be taken as the type. The 

 shell of Turbo is solid, and covered with a thick epi- 

 dermis. The convex whii'ls are often grooved or 

 tuberculated, and the aperture slightly produced in 

 front. The operculum is very solid, externally con ■ 

 vex, and covered with granules, and internally horny 

 and few-whirled. — (See fig. annexed, and Plate 3, 

 fig. 3.) The described species are about sixty in num- 



Fig. 222. 



Turbo olearius and operculum. 



ber, and are chiefly found in the islands of the Eastern 

 archipelago, Australia, New Zealand, &c. The shells 

 of nearly all are brilliantly pearly when the epidermis 

 has been taken off and the outer layer of shell removed. 

 THE TTTEBO OLEAEIUS (see fig. annexed) is used by 

 the trade in the manufacture of papier-mach(5 articles 

 and other ornamental goods where mother-of-pearl is 

 employed. The inner layer of this largo species is 

 beautifully iridescent, and is imported in considerable 



