GASTROPODS . 
347 
Other Families. 
may be from about twenty to forty days before the young snail eats through the 
skin or shell of the egg, and this it is said to entirely consume. Although H. 
pomatia is commonly styled the edible snail, it should be remembered that other 
species are also considered a delicacy; JI. aspersa, H. naticoides, and H. 
vermiculata being commonly eaten in parts of Italy and Sicily; while in Naples, 
II. ligata and H. lucorum are also to be seen for sale. H . mazzullii, which is 
collected near Palermo, possesses the power of boring into the rock; this being 
probably effected by means of the radula. The supposed object of these excava¬ 
tions is to secure a place of refuge during the period of excessive heat, and also to 
obtain a supply of lime for the formation of the shell. The Philippine Islands are 
the home of a beautiful genus of snails ( Helicostyla ), many of which are clothed 
with a peculiar periostracum, which, when wetted, becomes more or less transparent, 
disclosing the colour of the shell beneath. Two or three of the species are of a 
bluish tint, a colour not found among other land-shells. 
The important genus Bulimus (now abolished in favour of Stroplioclieilus) 
formerly contained a large number of species from all parts of the world, but is 
now limited to a comparatively few forms occurring in South America; S. oblongus 
being one of the commonest and best known species. Another, S. maximus, is 
sometimes as much as 6 inches in length. The majority of the other species, 
originally classed in Bulimus, are now located in Bulimidus and its sections, or in 
Bidiminus. These genera are distinguished by differences of the jaw and radula. 
There are several other families of land-shells, which can only 
be briefly referred to. The Cylindrellidce are very elongate, many- 
whorled shells, which occur principally in the West Indies and South America; 
many of them being remarkable for their slender forms and exquisite sculpture. A 
peculiarity of Cylindrella consists in the shell being almost invariably truncated, 
that is, the upper whorls are broken off when the animal reaches maturity. This 
may be done to lighten the shell, which otherwise would be too long for the 
mollusc to carry erect. The Pupidce comprises a number of forms which are 
conchologically very dissimilar. The typical Papa includes minute creatures, and 
appears to be found in all parts of the globe, but especially in temperate and 
mountainous regions. They are gregarious and live in moss, under stones, in the 
crevices of old walls, or among the roots of grass and other plants. Most of the 
species have what are called “ teeth ” within the aperture of the shell, and these in 
some species are so numerous as to almost close the opening, and 
thus make it, one would suppose, a matter of some difficulty for the 
animal to squeeze through them when emerging from its shell. 
Vertigo is a genus similar to Pupa as regards the shell, but separable 
on account of the animal having only one pair of tentacles, the lower 
pair being entirely wanting. The shells, according to the species, 
are dextral or sinistra! Clausilia is remarkable for the large 
number of species, the general similarity in the form of the slender 
shell, and the peculiar process within it, which serves as a door to 
shut in the animal when retracted. The shells are almost invariably reversed, and 
furnished with two or three folds or plicne within the mouth, and other lamelke 
still further within, which can only be detected by the transparency of the shell 
Clausilia. 
