Gasteropoda. MOLLUSCA. PALUDiNiDAi. 339 
slight canal in front. The operculum is horny, spiral. 
The species are numerous, about seventy having been 
enumerated, and are found distributed throughout all 
parts of the world. They are most abundant, however, 
in the north temperate zone, and live among sea-weed 
in shallow water. 
Family — MELANIIDJD. 
This is a numerous family, containing within it 
upwards of one hundred and sixty species. The shell 
is spiral, turreted, and covered with a dark olive 
epidermis. The aperture is ovate or circular, some- 
times entire in front and at others channeled ; and the 
operculum is ovate, horny, and spiral. The animals 
of this family are fluviatile, being inhabitants of fresh- 
water lakes and rivers throughout the warmer regions 
of the globe ; and the apex of the spire of the shell is 
often eroded by the action of the water in which they 
live. In the southern states of North America they 
are numerous and form peculiar groups. Some of 
the species are viviparous. The animal of one species, 
Melania amarula, is very bitter, and in the Isle of 
Bourbon and some of the adjacent islands it passes 
for an excellent remedy for the dropsy. The variety 
of form which characterizes many of the shells has 
necessitated their being grouped in different genera, 
and a good many have accordingly been formed. The 
principal character depended upon for dividing them 
is the form of the aperture. The family is represented 
in Plate 1, figs. 1 and 2, by Melania (bibex'; Byronensis. 
Family- CEKITHIID AH. 
The Cerithia have the shell ovate, spiral, many- 
whirled, and covered with a thin epidermis. The 
aperture is ovate or subquadrate, and more or less 
channeled in front. The ‘outer lip is often expanded, 
especially in adult specimens. The operculum is 
horny and spiral. The species are numerous, upwards 
of one hundred having been described, and they pre- 
sent various modifications of form and habits of life. 
Two forms are represented in Plate 1, figs. 1 and 2, 
by Cerithium Iceve and Tympanotomus muricatus ; and 
the operculum is represented by that of Telescopium 
fuscum in fig. 3. The operculum here offers a good 
character for assisting in separating them into groups. 
Some of the species are marine in their mode of life, 
while others dwell in the mouths of rivers or in salt 
marshes. Some of the marine species emit a green 
fluid when molested, which becomes purple in drying. 
“ Two specimens of Cerithium armatum were brought 
alive to London from the Mauritius,” says Dr. Johnston, 
“ kept, during their long voyage, in a dry state, 
affording a remarkable illustration of tenacity of life. 
The animal was apparently healthy, and beautifully 
coloured. It emitted a considerable quantity of bright 
green fluid, which stained paper of a grass-green 
colour. It also coloured two or three ounces of pure 
water. This green solution, after standing for twelve 
hours in a stoppered bottle, became purplish at the 
upper part ; but the paper retained its green colour 
though exposed to the atmosphere. A tincture made 
by immersing the animal of Cerithium telescopium in 
spirits, became of a dark verdigris colour, which it 
retained for some weeks.” These shells are found in 
all parts of the world, the typical species, however, 
being tropical. 
The fluviatile or salt-marsh species, forming the 
genus Telescopium, are few, and are found inhabiting 
the salt marshes and swampy tracks near the mouths 
of rivers in the East Indies and their islands. There 
they may be seen, with their pointed spires sticking 
out of the mud, in incredible numbers. We have 
seen them in great abundance on the muddy shores of 
Saugor island at the mouth of the river Hooghly in 
the Bay of Bengal ; and we are told that their numbers 
are so great that they are collected for the purpose of 
being burnt into lime. Great heaps are formed and 
exposed to the sun to kill the animals. In the island 
of Borneo the animals are eaten by the natives. 
Family— TURRITELLID^. 
The family of TURRET or SCREW SHELLS {Turri- 
tellidce) have the operculum horny, circular, and many- 
whirled, the whirls fringed on the edge. The shells 
are spiral, many-whirled, imperforate, and the aper- 
ture is rounded and simple in front. This is strictly 
a marine family; the species, which are tolerably 
numerous — upwards of fifty having been described — 
ranging from low-water mark to the depth of one hun- 
dred fathoms. Their geographical distribution is world- 
wide, one species living in our own seas. The term 
“ Screw-shells,” by which they are familiarly known, 
is derived from their peculiar spiral form. They live 
buried and fixed in tenacious mud, mixed with shelly 
debris, and can only protrude the head and tentacles 
from the mass. They walk very slowly, owing to the 
shortness of the foot. 
Genus Turritella. — This genus gives its name to 
the family, and contains a considerable number of 
species, the shells of which are turreted, and have a 
subquadrate-shaped aperture, simple in front. They 
are chiefly natives of tropical countries. 
Passing over the family BARLJEIDiE, the species of 
which are few, small, and obscure, we come next to the 
River Snails : — 
Family PALUDINID.® {Viviparidce). 
In this family the shell is spiral, turbinate, covered 
with an olive-coloured epidermis. The aperture is 
ovate and simple in front. The species of River 
Snails, amounting to upwards of sixty, are fluviatile, 
inhabiting lakes and streams over the greater part of 
the world. They have a good deal the external 
appearance of the Apple Snails {Ampullariidai). — See 
page 201. 
Genus Paludina {Viviparus). — This genus has 
a thin, horny, annular operculum, with the nucleus 
near the middle of the inner side — Plate 2, fig. 3. 
The shell is ovate, thin, and covered with a thin 
epidermis beset with hairy bands. The species inhabit 
the rivers and lakes throughout the Northern hemi- 
sphere. The animals are sluggish, feeding upon living 
