Neritinid^.' MOLLUSCA. TuRBiNiDiK. 343 
with spiral laminae. The axis is covered with a callous 
deposit. The species are from the West Indies, and 
are prett}', smooth, and shining shells of a yellow 
colour. They are terrestrial shells, and, like the 
Cyclostomidffi to he afterwards mentioned, they breathe 
free air. They have no operculum, and their dentition 
agrees with the other scutibranchiate genera. 
Family — NERITID.® = NeritinidjE, 
{The Nerkes.) 
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 oixler. They are 
littoral in their mode of life, being generally found 
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 flat 
beneath. The spire is lateral and very short ; the 
inner lip 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 Nerita. — The species of this genus are 
numerous, are all marine, and are chiefly found in 
warm or tropical seas. — See Plate 3, fig. 1 {Nerita 
undulata). 
Genus Neritina (= Neritella). — 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 
Nipah 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 opinion that this is catised by the animal’s filing 
off 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. cariosu). 
Genus Navicella (= 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 surface 
of the foot. — See Plate 4, fig. 1 {Terms used in Con- 
chology). The species, of which nearly twenty have 
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 rivers. In the island of Bourbon, the Navicella 
elliptica is commonly used to make a soup for the sick. 
Family— TURBINIDiE {Top-shells'). 
The Top-Shells 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 — affecting of course the 
shape of the shell — and by the form of the operculum. 
Group T. — Turbinina {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 Turbo may be taken as the type. The 
shell of Turbo is solid, and covered with a thick epi- 
dermis. The convex whirls 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 TITRBO OLEARIUS (see fig. annexed) is used by 
the trade in the manufacture of papier-machd articles 
and other ornamental goods where mother-of-pearl is 
employed. The inner layer of this large species is 
beautifully iridescent, and is imported in considerable 
