GASTROPODA. 17 



aperture of its shell into an elongate tube, in order to keep pace 

 with the growth of the coral, and to prevent its being overgrown 

 and killed. 



Fijr. 8. 



\ 



The Common Whelk (Buccinum undatum). 



a. siphon; b, foot; c, tentacles; d, eyes; e, operculum. 



The Olives (Olivldce) are common in most tropical seas, and are [Case 4, 

 remarkable for their beautiful polish and various patterns of colour- B 

 ing. In structure and form they are very similar to each other. 

 They burrow in sand in quest of bivalves for food, and some species 

 are said to have the power of swimming by expanding the lobes of 

 the foot. 



The Harps {Harpidce) form a small well-marked group, of which i Case 4. 

 probably all the existing species have been discovered. The animals D ~ E -] 

 inhabiting these beautiful shells are also brightly coloured. They 

 have the remarkable power of casting off a portion of the foot when 

 disturbed. The species are known from the Indo- Pacific Ocean, 

 the west coast of Central America, and West Africa. 



The Fasciolariidee contains one of the largest living Gastropods [Case 4 

 (Fasciolaria gigantea) , which is found off the coast of South Carolina, E ~ G -] 

 and attains at times a length of two feet. 



The Mitras (Mitridce) are great favourites with shell-collectors, [Cases 

 on account of their beautiful colours and varied sculpture. There 4h-5b.] 

 are about 600 living species already known, and between one and 

 two hundred have been found in a fossil state. Shells of this 

 group, like the Fasciolaricp, are distinguished by a few plaits or 

 folds on the inner side of the aperture (the columella) . Mitras 



