352 



THE OCEAN WORLD. 



in turn been ascribed to the presence of copper pyrites in the neigh- 

 bourhood of the mu?sel ; to certain small crabs which lodge themselves 



as parasites in the shell 

 of the mussel; to the 

 spawn of star-fishes or 

 medusfB that the mus- 

 sel may have swallowed. 

 But, probably, the true 

 cause of this kind of poisoning resides in 

 the predisposition of individuals. The 

 remedy is very simple: an emetic, ac- 

 companied by drinking plentifully of 

 slightly acidulated beverages. 



We have now come to the twentieth 

 family, the Aviculidse, which contains 

 Avicula, Malleus, Malapgrina, Perna, and 

 Pinna. The shells of the Hammerheads 

 (Malleus) have a rough resemblance to 

 the implement from which they derive 

 their name. The valves are nearly equal, 

 blackish, and somewhat wrinkled on the 

 exterior, often 

 brilliantly nacred 

 in the interior. 

 They are enlarged 

 to the right and 

 left of the hinge, 



forming prolongations on each side, 

 which give them the fancied . resem- 

 blance to the Hammerhead (Fig. 163). 

 At the same time they grow in a direc- 

 tion opposite to the hinge, which gives 

 something approaching the handle of 

 the implement. 



This is the first feature which a 

 glance at Malleus alba (Fig. 162) con- 

 veys. The hinge is without teeth, 

 having instead a deep conical fossette or dimple, for the reception of a 



Fig 162. Malleus alba (Lamarck). 



Fig. 163. Malleus vulgaiis (Lamarck\ 



