14 



SHELL GALLERY. 



Oases 

 25-26. 



Oases 

 27-28. 



Oases 

 31-32. 



placed at the base of the tentacles instead of at theh' tips, they 

 have a long proboscis armed with a different rasping tongue {raduld), 

 a spiral operculum, and the sexes are distinct, whereas the true 

 Snails are hermaphrodite. 



The operculated air-breathers have been divided into many 

 sections, chiefly on account of differences in the apertures of the 

 shells and in the opercula. They most abound in hot countries, but 

 a few species are met with in temperate regions. 



The "Apple-Snails" {AmpuUariidce) live in the rivers and 

 marshes of tropical regions, and, although represented by a large 

 number of species, exhibit comparatively slight variations in form 

 and colour. The animal has both a pectinated gill and a lung 

 cavity, being thus enabled to breathe either water or air. 



Fig. 8. 



32-35. 



Ampullaria canaliculata. 



The " Periwinkles " {Littorinidce) are found almost on every 

 known shore ; they feed upon all kinds of marine vegetation. 

 Some species are met with at low-water mark, others on rocks 

 almost beyond the reach of the sea, and some have been discovered 

 inland nearly half a mile away from the shore. It is calculated that 

 1900 tons of the "Common Periwinkle" {Littorina Uttot'ea), of the 

 value of £15,000, are annually consumed in London alone. 



The family of CalyptrcBidce. includes the " Slipper-Limpets " 

 {Grepidula) and the " Cup-and-saucer Limpets " {Crucibulum). 

 Although furnished with a foot, they rarely crawl about, but 

 remain attached to rocks, stones, or other shells, sometimes 

 forming a shelly plate under the foot by which they become 

 fixed to the spot where they have taken up their abode. 



The " Cowry-shells " {Cyprce^idce) are remarkable for their varied 



