Gasteropoda.- 
MOLLUSCA. Littokinid.®, 
337 
curopaa) is a plain white shell, but its snail is a ver}' 
elegant creature The proboscis is dark vermilion; 
the tentacula yellowish-red, spotted with yellow ; the 
upper part of the foot streaked longitudinally with 
yellow and brown ; and the mantle greenish-brown, 
edged with brownish-red ; but, notwithstanding, the 
shell is a uniform dull white.” — {Johnston.) 
Family — APOERHAIDJE. 
The family of Spout-shells {Aporrliaidm) have the 
shells spiral when adult, and the canal is bent to the 
right. The outer lip is expanded or revolute, some- 
times lobed or digitated. The operculum is annular, 
ovate, or pointed, with a small apical nucleus. 
Genus Aporuhais. — This genus, which gives its 
name to the family, has the shell fusiform, the spire 
elongated, with many tuberculated whirls, a narrow 
aperture, a distinct canal, and the outer lip dilated 
and lobed, or digitated. The operculum is ovate 
pointed, and lamellar. There are only three species 
known, two of which are natives of Great Britain and 
the Mediterranean, and one of Labrador. 
THE APOKRHAIS PES-PELICAHI, or Pelican’s 
Foot, is very common in Great Britain. The animal 
creeps slowly, and is shy in its disposition. The shells 
are subject to great variety with respect to the outer 
lip. In the young shell there is not the least expansion 
of the lip, but it increases by age. It is generally of 
a dull white colour; but the animal has its rostrum 
pink, dotted over with milk-white spots ; the tentacles 
are also of a pink colour, and the eyes black. 
Genus Struthiolaria. — The genus Struthiolaria, 
or Ostrich’s-foot shell, is more numerous in species 
than Aporrhais, but they are exclusively confined to 
New Zealand and Australia. The shell is ovate, with 
a conic, acuminated spire. The aperture is ovate, with 
a short indistinct canal in front, and the lips and 
columella are thickened and polished. The operculum 
is ovate, acute at the apex, with a broad notch on the 
inner side near the tip. 
Genus Trichotropis. — This genus is composed of 
top-shaped spiral shells, with keeled whirls, which are 
edged with a horny fringe, and covered all over with 
an epidermis of the same substance. The species, 
which, are few in number, are chiefly from the northern 
seas, where they inhabit deep water. 
In the preceding families of the Rostrifera, the 
mantle of the animal, when full-grown, is expanded, 
and more or less reflexed over the shell. In those 
which follow, the mantle is inclosed withiri the shell. 
Some of them are inhabitants of the dry land, and 
their breathing organs are adapted for respiring free 
air. They are vascular, branched, and are placed on 
the inner surface of the mantle, which is free from the 
nape, and leaves the pulmonary cavity open. The 
animals have distinct sexes, are oviparous, and possess 
a well-formed spiral or annulated operculum. 
Family— CYCLOSTOMlDiE ( Cyclophoridce). 
The animals belonging to this family have an elon- 
gated foot and a spiral operculum. This operculum pre- 
Von. IT. 99 
sents several modifications of structure, which are found 
to be characteristic of several groups, into which this 
numerous family may he divided. In some it is thickish, 
and more or less shelly ; in others it is thin and horny. 
The animals of this extensive family, numbering be- 
tween four hundred and five hundred species, are either 
found in the humid parts of tropical forests, some 
concealed amongst the debris at the roots of trees, 
others creeping on the branches and foliage, or they 
are met with in dry and arid situations, among loose 
stones and leaves, in chalky regions. The shells are 
usually turbinate, and are generally covered with an 
epidermis, which is often mottled or variegated with a 
reddish-brown colour. The form of the shell presents 
many modifications, as well as the operculum, and the 
two together afford valuable aids in grouping the various 
species. 
Family — HELICINID.1E {Oligyradce). 
This family consists of terrestrial, air-breathing, 
operculated shells, like the preceding family, Cyclos- 
tomidce. The animals scarcely differ at all in structure 
from, and in their habits they are very similar to, those 
of that family. The shells differ chiefly in their aper- 
ture being semilunate, and in the operculum not being 
spiral. In some this operculum is thick and shelly, in 
others thin and horny. In common with several other 
mollusks, the Helicinidae possess the power of absorbing 
the columella and the internal divisions between the 
upper whirls. 
The genus Helicina has a membranaceous or shelly 
operculum, and a turbinate, globose, or depressed shell, 
with a triangular or semi-ovate, entire aperture, and a 
callous base. The species, which are numerous, are 
chiefly natives of the West Indian islands and tropical 
America, a few also being found in the Philippine and 
Pacific islands. 
The two preceding families, as we have said above, 
are terrestrial in their habits. The three following are 
what may be called amphibious in their manner of 
life. The respiratory organs, or gills, are disposed in 
very numerous cross folds on the inner surface of the 
mantle. 
Family — LITTORINIDiE {Periwinldes). 
The family of Periwinkles have a spiral, turbinated, 
or depressed shell, with a rounded, entire aperture, 
never pearly within. The operculum is horny, spiral, 
of few whirls. The animals possess two gills, one of 
them very large, occupying nearly the whole surface 
of the bronchial cavity, and formed of numerous flat, 
free plates. 
Genus Littorina. — This genus has a thick shell, 
pointed, and composed of only a few whirls. The axis 
is imperforate, and the apertures subcircular and entire. 
The columella is rather flattened, and the outer lip 
acute. The animals have a very long tongue, that of the 
Common Periwinkle {L. littorea) being two inches in 
length. The species are numerous, upwards of forty 
having been described, and they are found on the sea- 
shore in all parts of the world. They are amphibious 
