152 MOLLUSCA 



are found in shallow water, and are used as bait and for food. 

 One Pacific coast species reaches a length of eighteen inches. 



Class 3. Gastropoda. — The Gastropoda differ from the Lamelli- 

 branchiata considerably, in that they usually have a spirally coiled 

 shell consisting of a single piece, a head region with eyes and sensory 

 tentacles, and in the alimentary canal have a buccal organ, the 

 odontophore^ bearing rows of chitinous teeth and functional in rasping 

 food and in cutting through other shells. Gastropoda creep slowly 

 on a ventral foot, which in the marine snails carries a horny opercu- 

 lum used in closing the orifice when the foot is retracted. 



The chank-shell {Turbinella pyruni) , found in the Indian Ocean, 

 is used in the East Indies for bangles. When cut into armlets and 

 anklets, chanks are worn by the women of Hindustan. Chank- 

 shells were also used for beating cloth. The whelk {Buccinum) is 

 eaten by some Europeans. Another whelk {Purpura) was used 

 by the ancients in the production of " Tyrian Purple." The 

 Romans secured their dyes from shells found off the coast of Tyre 

 in Asia, and at Meninge on the shore of Africa. Pliny speaks of the 

 mixture of dyes of different shades to produce the finest purple for 

 royal robes. The slipper limpets {Crepidula Jornicatd) are de- 

 generate scale-like animals that in many cases become attached 

 permanently to a stone or dead shell by a stony cement secreted by 

 the foot. The embryology of Crepidula was the subject of an 

 authoritative study by Conklin (Jour, of Morphology, vol. 13, 1897). 

 The common limpet {Patella vulgata) is used as food in England and 

 on the Continent much more than in the United States. The ear- 

 shells ( Haliotis) found on the Western coast of America appear like 

 the single valve of a Lamellibranch, but they are true gastropods. 

 The shells are used for the manufacture of ornaments, in inlays 

 and also for making buttons. They also yield blister pearls of 

 brilliant colors. The fleshy foot of the animal is an excellent food, 

 which has been eaten in Europe and the Orient for centuries, and 

 furnishes abalone steak in California. It is also dried and shipped 

 to the Orient. The cowries {Cypraeidae) are used for ornaments, 

 to sink fishnets, and as money. A small species {Cypraea moneta) 

 is used in Siam and Western Africa as money. Lankester mentions 

 the fact that in the Friendly Islands the orange cowrie, a symbol of 

 rank, is worn only by the chief of the tribe. 



The helmet shells {Cassidae) are used in the manufacture of 

 cameos^ since either white or black may be carved with the other as 



