404 SNAILS, OR HELICID^. 



are armed, and which, when the creature contracts itself, give it a curious resemblance 

 to the hedgehog. Its colour is reddish brown on the exterior, and pinky white within. 

 Although this shell attains a ver/y great size, a large specimen measuring about five 

 or six inches in length, it is not as valuable as in its youth, the curious spines being 

 gradually lost as it approaches old age, just as human beings lose their hair, and 

 the shell being by degrees rubbed tolerably smooth in some places and encrusted in 

 others with corallines, calcareous matter, and the shelly coatings of various marine 

 zoophytes. Sometimes the seaweeds find a lodgment on the shell, as is often the case 

 with other comparatively stationary molluscs, such as the common limpet ; and in that 

 case the algse not only find a home, but conceal their protector by their waving fronds. 



THE smaller and smooth figure represents the MAKBLED CHITON, a rather prettily 

 coloured shell, its exterior being rusty red mixed with brown and yellow, and edged with 

 brown. The SHORT-SPINED CHITON may be seen with the shell covered with short spines, 

 and partly turned up so as to show the head of the animal. Its colour is sooty black, 

 but this dull uniformity of a sombre hue is more than redeemed by the beautiful 

 and minute pencilling with which its surface is engraved. The last figure represents 

 the BANDED CHITON, or CHITONELLA, a creature that has been removed by modern 

 naturalists into a separate genus on account of the formation of the armour. The plates 

 do not cover the entire s\irface as in the preceding genus, as only a portion is seen above 

 the mantle. The defence is, however, nearly as perfect as in the previous genus, as the 

 projections approach each other beneath the surface of the mantle, and would act as 

 effectually in shielding the internal organs as if the plates had met on the surface. 

 These creatures are generally found in the clefts of canal rocks. 



The animal is more active than that of the limpet, but does not appear to be very 

 locomotive in its habits. Its broad creeping disc adheres very strongly to the rocks, and 

 holds the animal so firmly that, if it should happen to have taken up its abode within 

 a crevice, to extract it without tools would be an impracticable task. Like the 

 dentalium, this creature possesses neither eyes nor tentacles. 



PASSING from the sea to the land, we come to those gasteropods which breathe 

 atmospheric air, and are furnished with respiratory organs suited to the lower element 

 in which they live. These creatures fall naturally into two large sections, the one being 

 destitute of an operculum and the other possessing that remarkable appendage. They 

 are respectively called inoperculate and operculate gasteropods, and it is with the former 

 that we have now to deal. The inoperculate are generally furnished with large shells ; 

 but in some, such as the slugs, the shell is either very small or wholly absent. The 

 shell of these animals, when present, is not nearly so hard and porcelain-like as that of 

 the sea-snails, and contains a much larger proportionate amount of animal matter. It is 

 worthy of notice, that in order to prevent the waste of moisture in those species which 

 live on land, and the entrance of water in those which inhabit the ponds and rivers, the 

 respiratory passage is small, and closed with a kind of valve. 



THE first family is that of the Snails, or Helicidae, containing a vast number of species. 

 Most of the Snails have a shell large enough to permit the animal to withdraw itself 

 wholly into the protecting domicile. During the time when they are active these 

 creatures require no closure of their shells, and accordingly have no vestige of an 

 operculum, as may be seen by looking at a common Snail. In the winter, however, when 

 they retire from active life, and need that the aperture of their domicile shall be closed, 

 the place of the operculum is supplied by a layer of hardened mucus, sometimes 

 strengthened with the same substance of which the shell is composed, and always being 

 perforated with a little hole to permit the inhabitant to respire. Any one may see this 

 structure, called technically the epiphagus, by examining a Snail drawn from the crevice 

 .n which it ensconces itself during the winter months. 



The animal has a rather short head, furnished with four tentacles, the upper paii 

 being the largest, and bearing at their tips the little black specks which are supposed to 



