GASTROPODA. 



19 



ave found floating about in every ocean, with the spire of the shell 

 downwards, and the bottom, being more exposed to the action of 

 light, is more deeply tinted than the upper part. They feed upon 

 Jelly-fish, and construct a gelatinous raft, filled with air-bubbles, 

 beneath which the females attach their eggs. 



A large section of the Gastropods, commencing with the ' ' Apple- [Cases 

 Snails" (Amp till aril da) and ending with the " Carrier- shells " 6h-9h.J 

 (Phorida), are mostly vegetable-feeders, and, unlike the preceding 

 families, have a proboscis or snout, which is not retractile. 



The "Apple-Snails" {Ampullar li die) live in the rivers and [Cases 

 marshes of tropical regions, and, although represented by a large 6h-7aJ. 

 number of species, exhibit comparatively slight variations in form 

 and colour. 



Of the Ovulidce, the most curious is the " Weaver's-shuttle " [Case 7 b.] 

 (Radius volva), in which the shell is peculiarly beaked at both 

 ends. It is found living on barked corals (Gorgoniida), and some 

 of the smaller species exhibit differences of coloration, resembling 

 the tints of the Gorgonias upon which they are found. 



The "Cowry-shells" (Cyprceida) are remarkable for their 



[Case 7, 



B-E.] 



Fi<?. 9. 



The Tiger Cowry (Cyprcea tiyris). (From the Indo-Pacific Ocean.) 

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



ff, eyes. 



varied 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 



