CHAPTER XIV. 

 BIVALVES AND CUTTLES. 



General characters of Bivalves Their classification The saddle-oyster 

 and the mussels Their structure and habits Oysters, Pectens, 

 and Lima Swimming power of Pecten and Lima Characters of 

 Cyprina Mactra and its allies The Venus and carpet-shells 

 The cockles The gapers Mya and Lutraria Rock-borers The 

 cuttles. 



THE next great group of the Molluscs is constituted by 

 the Bivalves, or Lamellibranchs ("plate-like gills"), of 

 which the oyster, mussel, and clam are familiar examples. 

 In order to get a notion of the anatomy, it is well to obtain 

 a living mussel and a living example of the bivalve known 

 as the little carpet-shell (Tapes pullastra), which is very 

 abundant on the rocks. The blue shells of the former, 

 and the brownish yellow ones of the latter, are very 

 common objects on most shores. Place both in water, and 

 notice the two valves of the shell, united to one another 

 by an area of greater or less extent known as the hinge. 

 Notice that when the animals are at rest the valves gape 

 slightly, allowing certain of the soft parts to protrude. But 

 when alarmed they close their shells suddenly, sometimes 

 sending out a sudden jet of water in the process. The way 

 in which the shell is closed enables you to conclude at once 

 that it must be the result of muscular action ; there are, in 

 fact, large closing muscles, usually two in number, in all 

 Bivalves, and they are very characteristic structures. 



Next study carefully the parts protruded in an open 

 bivalve. Take the mussel first (see Fig. 77). As the shell 

 gapes there appears at the part of the shell opposite the 

 hinge a fringed mantle-flap (i in Fig. 77), which is double 



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