GASTROPODA. 



15 



markings and splendid polish, which is produced and preserved by 

 two flaps of the mantle, one on each side, which fold over the back, 

 a line down the centre of which usually marks 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 



Fisr. 9. 



The Tiger Cowry {Cyprsea tigris). (From the Indo-Pacific Ocean.) 



a, the shell ; h, the mantle ; c, foot ; d, siphon ; e, proboscis ; /, tentacles ; 



<7, eyes. 



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-cowry " {G. 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 specimen 

 of Gyprcea leucodon figured on p. 16 is extremely valuable and sup- 

 posed to b3 the only one hitherto discovered. The " orange cowry " 

 (Cyprma aurora) is worn by chiefs in the Friendly Islands, and is 

 considered the highest order of dignity. Only one small species, 

 Trivia europcm, is found on the British coast, and numerous fossil 

 forms have been discovered in Jurassic, Cretaceous, and Tertiary 

 rocks. 



Of the OvulidcB, the most curious is the " Weaver's-shuttle " Case 35. 

 {Radius volva), in which the shell is peculiarly beaked at both ends. 

 It is found living on barked corals {Gorgoniidce,), and some of the 

 smaller species exhibit differences of coloration, resembling the tints 

 of the Grorgonias upon which they are found. 



The Naticas are mostly blind, and have a very large foot, suitable Cases 

 for burrowing in the sand when in quest of bivalves. They are very ^^~°''^- 



