A VIC ULA RID^. 847 



other materials, by means of the silken threads or "byssus" which it is capable of secreting. 

 It often appears almost entirely buried in the mass of nullipores which it has gathered around 

 its shell. The long tentacular appendages are kept in constant movement, possibly without 

 the will of the animal, keeping iip their writhing contortions just as our hearts continue to 

 beat without our knowledge. Even after the death of the animal, and when they have been 

 separated, the filaments continue to move, twining and twisting like so many worms. 



The File-shell can pass through the water with some rapidity, urging itself along by the 

 sharp closing of its valves. Its color is crimson, with the exception of the mantle, which is 

 orange. The shell is pure white, so that a living and healthy specimen is a most beautiful 

 creature. 



A very curious example of this family is found in the THOKNY OYSTER, a species that is 

 remarkable for the singularly long projections from the shell. The object of these spines is 

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

 insiduous 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 group including the curious Spondylus, with its numerous projecting processes, also 

 embraces the Malleus, or Hammer-shell, and the Lithodomus, or stone-borer, and the Modio- 

 lus, a large mussel-like shell, of our shores. 



The UnionidcB rank next, the family embracing the large number of fresh-water shell- 

 fish, ranging from the small unios of our creeks and rivers to the great bivalves of the western 

 waters, lakes and rivers. 



Family iMcinidce embraces some small circular shells, prettily ornamented by concentric 

 ridges. Two species are found on our coast. It is a singular fact, that certain shells are so 

 confined to special localities, and that some are so exceedingly scarce, unless indeed some 

 cause has been actively at work to decimate them. The Lucinia radula is an example of 

 both these conditions. On Chelsea Beach, in Massachusetts, broken valves of this shell are 

 occasionally seen ; but only one perfect shell, with the animal in it, was found up to the time 

 William Stimpson published his work on the marine shells of Massachusetts. This example 

 of Lucinia we now have before us. It was figured by Stimpson, and recorded standing lonely 

 as the only perfect example found on our coast. The Lucinia resembles the Cytherea above 

 figured. 



The CyprinidcB are represented on our shores by the large bivalve called Quahog, or 

 Round Clam, very much resembling the Venus, but larger, and having an epidermis covering 

 of greenish-brown, the Cyprina islandica, although the Venus mercenaria, is the proper 

 Quahog of the Indians. 



The pretty little chestnut Astarte is one of the most attractive of our bivalves ; about the 

 size and exactly the color of a chestnut, and not very unlike it in shape. 



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 finally 

 settles down in life, it acts like weak-minded men, and molds 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 serpulge, it had accumulated itself to them in the most curious man- 

 ner, 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 dis- 

 posal are as variable as the form. 



THE next family are termed Wing-shells, or Avicularidse, because the apices, or "um- 

 bones," as they are called, are flattened and spread on either side, something like the wing of 



