GASTROPODS. 347 



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; H. aspersa, H. naticoides, and H. 

 vermiculata being commonly eaten in parts of Italy and Sicily ; while in Naples. 

 H. 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 Strophocheilus) 

 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 ; 8. 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 Bidimus, are now located in Bulimidus and its sections, or in 

 Buliminus. These genera are distinguished by differences of the jaw and radula. 



There are several other families of land-shells, which can only 

 Other Families. . 



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 Pupa 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 sinistral. 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 plicae within the mouth, and other lamellae 

 still further within, which can only be detected by the transparency of the shell 



