20 



SHELL GALLERY. 



where the flaps meet. The animals are even more brilliantly 

 coloured than the shells. They have no operculum, but a large 

 foot, which they can withdraw entirely within their shell, although 

 the aperture is usually very narrow. Cowries, as is well known, 

 are sold as ornaments ; and a small yellow species, " the money- 

 cow n '' (C. moneta), which is very common in the Indian and 

 Pacific Oceans, passes current as coin among the negro tribes of 

 certain parts of Africa. The "orange cowry " {C. aurora) is worn 

 by chiefs in the Friendly Islands, and is considered the highest 

 order of dignity. Only one small species, C. europaa, is found on 

 the British coasts, and about 100 fossil forms have been discovered 

 in the Chalk. 



[Cases The Cyclophoridce and Helicinidce are land- shells, which, 



however, cannot properly be considered true lung-breathers like 

 ordinary Snails. They have not the closed lung-chamber of the 

 Pulmonates, their eyes are placed at the base of the tentacles 

 instead of at their tips, they have a long proboscis armed with a 

 different rasping tongue (odontophore), 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. 



[Cas The "Periwinkles'" (Littorinidce) are found almost on every 



' J 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 

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

 1900 tons of the "Common Periwinkle" {Liitorina littorea), of 

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



[Case 3, The Melaniidee are freshwater Snails which abound in most 



C ~ F -J tropical and subtropical countries; about 1000 species are known. 



They are mostly of dark colours, and are fond of muddy places. 



[Case 8, The Cerithiida are chiefiv marine forms, some, however, entering 



G-H.l 



brackish water. About five hundred fossil species have been 

 described, some of them gigantic in comparison with any now 

 living, of which more than two hundred are known. 

 [Cases The " Screw-shells " {TurriteUidce) have elongate tapering shells; 



