404 SNAILS, OR HELICID.E. 



plates are armed, and which, when the creature contracts itself, give it a curious re- 

 semblance to the hedgehog. Its color is reddish brown on the exterior, and pinky white 

 within. Although this shell attains a very 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 coralines, 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 

 algae not only find a home, but conceal their protector by their waving fronds. 



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

 colored 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 color 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 armor. The 

 plates do not cover the entire surface 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 disk 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 at- 

 mospheric 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, some- 

 times 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 in which it ensconces itself during the winter months. 



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

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



