Achatixa MOLLUSCA. Lymn^a. 355 
occurred, where they have remained in a state of deep 
slumber for the space of twenty months. Their eggs are 
sometimes very large, and are covered externally with a 
hard calcareous shell. Those of Bulimus hcemastomus 
are almost as large as a pigeon’s, and nearly as hard. 
It appears that the tropical, and more especially the 
arboreal species, cement leaves of trees together, curl- 
ing one upon another, so as to form an artificial nest 
for the reception of these large eggs. 
Genus Achatina. — The Agate shells have a shell 
a good deal resembling the Bulimi ; but they are thinner, 
and the columella is twisted, and more or less abruptly 
truncated in front. The shell is not umbilicated ; the 
aperture is oval, elongate, and the peristome is thin, 
acute, and not reflected, the margins united by a dif- 
fused callus. The Achatinae are numerous in species, 
upwards of one hundred and twenty having been de- 
scribed, and some of the African ones are the largest 
terrestrial shells known. They attain the length of 
eight inches, and their eggs, which are calcai'eous like 
those of the Bulimi, are sometimes more than an inch 
in length. They are chiefly found about trees near 
water, and the great majority are natives of Africa. The 
genus is represented on Plate 7, fig. 8 (A. Virginia). 
Genus Pupa. — The Pup® have a solid, cylindrical, 
or oblong-ovate shell, with many whirls, a conical apex, 
and a rounded, often toothed aperture. The base is 
rimate or, rarely, umbilicated, and tbe surface of the 
shell is generally verj^ closely ribbed with straight ridges. 
The species are numerous, amounting to upwards of 
one hundred and sixty, and are found in all the four 
quarters of the globe. The genus is represented on 
Plate 7, fig. 9 {Pupa mumia). 
Genus Clausiha. — The Clausilias have a fusiform 
shell, almost alwa 3 's sinistral, or turned to the left. 
The aperture is elliptical or pyriform, provided with 
two plaits or lamell® which contract the margin, and 
is closed at the bottom, or in the neck, by a movable 
shelly plate, called a clattsium. This peculiar organ is 
attached to the pillar of the shell by a slender pedicel, 
and is placed in such a position as to shut the throat 
of the shell, when the animal is inclosed, while at the 
same time the animal can push it on one side, when it 
wishes to come forth in search of food. The species 
are very numerous, upwards of two hundred having 
been described, and are distributed over the four quar- 
ters of the globe, though most numerous in the tem- 
perate countries of Europe. This genus is represented 
on Plate 7, by fig. 7 {Clausilia cmrulea). 
Genus Cylindrella. — The Cylinder shells differ 
from the Clausilias, chiefly in wanting the plaits or 
lamell® in the aperture. The shells are generally long 
and cjdindrical, many-whirled, the apex in the adult 
generally broken off ; or truncated while the mouth is 
round, and the peristome expanded and continuous. 
Limnophila, Fresh-water Snails. — The animals 
belonging to the second group have subcylindrical or 
flattened tentacles, which are simply contractile, and 
have the eyes placed sessile on their base. 
Family— AURICULID^. 
The Auriculas have a ringed conical muzzle, and a 
thin mantle with a thickened edge. The shell is spiral. 
covered with a horny epidermis, and has the mouth, 
which is elongate, furnished with strong plaits on the 
columella. The outer lip is also in many cases toothed, 
or transversely ribbed. The animals are peculiar in 
having the power of absorbing progressively the septa, 
or divisions, which separate the cavities of the whirls 
from one another. With few exceptions the species, 
which are numerous (upwards of twm hundred having 
been described by Pfeiffer in the Catalogue of Auri- 
culidce in the collection of the British Museum), are 
natives of tropical countries, and live in brackish-water 
marshes, estuaries, and mouths of rivers, clinging to the 
stems and roots of mangroves; among loose stones above 
high water mark, but within the influence of the tide ; 
or in damp woods near the sea. 
Family — LYMN iEID.®. 
The Pond Snails have a short dilated muzzle, flat- 
tened tentacles, and a flattened, lanceolate, or oval foot. 
The shell is thin, horn-coloured, rather varied in form, 
but usually with an oblique fold on the columella, and 
a simple, acute outer lip. The species are numerous, 
and are all fresh-water animals, living in the water, but 
coming to the surface to breathe. They are found in 
all parts of the world, and inhabit ponds and running 
streams. They are chiefly found in temperate coun- 
tries, and are for the most part phytophagous or veget- 
able feeders. They deposit their ova on the stems and 
leaves of the weeds, which grow around them, enveloped 
in an oblong gelatinous nidus. The form of the shell, 
as we have said, is very varied. 
Genus Lymnaja. — The Lymnmae have a spiral, dex- 
tral shell, more or less elongated, thin, horn-coloured, 
and translucent. The last whirl is large, ventricuse, the 
aperture large, rounded in front, the columella obliquely 
twisted, and the outer lip simple and acute. The species 
are upwards of fifty in number, and are found in most 
temperate countries of the globe. Their food consists of 
both vegetable and animal matter, one species feeding 
on the green fresh-water alg®, while others prefer animal 
food. This peculiarity in their diet has caused them 
to be denominated “ the scavengers of the waters;” and 
Mr. Jeffreys informs us, that in the absence of other 
nourishment, “ they will even devour each other, piercing 
the shell near its apex, and eating away the upper folds 
of its inhabitant.” Although generally to be seen 
creeping on the muddy bottoms of ponds and streams, 
and on the stones, or on the leaves and stems of sub- 
merged plants, they always come to the surface to 
respire free air, and can, when there, to use Dr. John- 
ston’s words, “ make the water a liquid pavement,” along 
which they creep by an undulatory motion of the foot, 
but with the body and shell in a reversed position. 
“ When thus suspended, they will sometimes relax their 
hold and drop at once to the bottom, from which in 
general they emerge by crawling up some solid body ; 
but occasionally I have seen them rise up direct through 
the water.” — {Johnston.^ When the ponds are dried 
up, the Pond Snails bury themselves in the mud, 
strengthen the outer lip by an internal rib, and cover 
the mouth by means of a membranaceous epiphragm, 
like the land snails. 
