422 



THE HAMMER-SHELL. 



spines is rather obscure, but is said to answer a double purpose, the one being to act as 

 a chevaux-de-frise, whereby the attacks of marauding fish or other foes may be repelled, 

 and the other to aid in fixing the animal to the spot on which it has established itself. 

 Any fish, however, that would be strong-jawed enough to crush the shell, even without 

 the spikes, would care no more for them than does a donkey for the prickles of a 

 thistle ; and the smaller and more insidious enemies would receive no check from the 

 hedgehog-like array of bristling points. The animal of the Thorny Oyster is eatable, 

 and in many places is looked upon as a delicacy. 



The last example of this family is the HINNITES, a shell remarkable for its exceeding 

 variability of form. When young, it wanders freely through the ocean ; but when it 



HINNITES.-///fln/tes pusll. 



PINNA.-P/nna pectlnata. VARIEGATED SCALLOP.-Pecten vartos. 



NAMMER-SHELL.-;Ma//eus vulgaris. 



finally settles down in life, it acts like weak-minded men, and moulds itself to the 

 locality in which it happens to reside. If it gets among scoriae, as is not unfrequently 

 the case, the shell follows all the irregularities of its resting-place; and in one instance, 

 where one of these shells had settled upon a group of serpulae, it had accumulated itself 

 to them in the most curious manner, actually overlapping the shell so as to form its 

 edge into the half of a hollow cylinder. The colors are red, brown, and white, but 

 their relative amount and the manner of their disposal are as variable as the form. 



THE next family are termed Wing-shells, or Avicularidae, because the apices, or 

 " umbones " as they are called, are flattened and spread on either side something like 

 the wing of a bird. The interior of the valves is pearly, and the exterior layer is composed 

 of a kind of mosaic work of five or six sided particles. This structure is easily 



