254 



SUBKINGDOM MOLLUSCA. 



to cover up with nacre any irritating substance, as a grain of 

 sand, that may have gotten beneath the mantle.* 



The Hammer Oyster of the Indian Ocean presents one of 

 those singular forms seemingly designed to puzzle natural- 



Fig. !<36. 



Malleus viilgftris, Hammer-oyster. 



ists in endeavoring to account for the utility of the anomalous 

 appendages. 



other like shingles, each one indicating a season's growth and the series showing 

 the oyster's age. In three or four years a marketable size will be reached. The 

 little red crab often found sharing the oyster's home is the Pinnotheres ontrSum. 

 The female is generally seen, as the male is scarce. The latter has its back 

 ornamented with a white figure very like an anchor. At the discovery of America 

 the oyster was abundant upon the Atlantic coast. Immense mounds of shells lie 

 along the shore, from Maine to Florida. They antedate the time of the Indian, 

 and are so large that in Florida, during the late war, some were used as forts. 

 See Lockwood's" Natural History of an Oyster," in Popular Science Monthly, Novem- 

 ber, 1875. 



* Taking advantage of this, the Chinese have long been in the habit of producing 

 pearls artificially by slipping metal images under the mantle and then releasing the 

 animals. In six months the figures are found overlaid with a pearly secretion. 

 Sometimes, however, the crafty Celestials paste these images upon the interior of a 

 dead shell and then paint it, over with a mixture of powdered a mother of pearl," in 

 exact imitation of the genuine. 



