420 THE LIMA, OR FILE-SHELL. 



like the tiles of houses, and are at all times ready to be taken from the bed and sent to 

 market. 



This process possesses a double value, inasmuch as an oyster-bed, if left to itself, 

 would increase to such an extent as to endanger navigation ; and these inland banks are 

 always accessible, whatever may be the weather. In some cases, when confervoid growths 

 are rife, the Oysters attain a decided green hue, and are thought very valuable by 

 connoisseurs in such matters. In all improvements, however, there is always some 

 drawback. The Oysters produced by artificial culture are acknowledged to be fatter and 

 finer than those which are suffered to grow in the open seas ; but their artificial size is 

 said to be a poor compensation for their comparative want of flavour, the artificially bred 

 Oyster being to the marine mollusc what the capon is to the pheasant. 



In the sea, thousands of Oysters perish by the attacks of a strange enemy. TLe 

 reader has doubtlessly remarked that the shells of many Oysters are partially perforated 

 by little round holes. These are the marks left by a kind of sponge, called Cliona, 

 which burrows into and gradually destroys the shells of this mollusc, causing them to 

 fall to pieces by its ravages. 



In the centre of the engraving on the previous page is seen a species of the genus 

 Ostrea, which is remarkable for its very long hinge. 



THE uppermost figure represents the CHINESE WINDOW-SHELL, a curious and rather 

 valuable shell, which is found in the country from which it takes its name. 



This shell is extremely flat, and of a beautiful translucence, and in many parts of 

 China is employed for windows, just as is ground-glass among ourselves, the nacreou^ 

 substance permitting the light to pass through, but effectually preventing an inquisitive 

 eye from distinguishing objects within the apartment. Very small pearls are found in 

 this shell, too minute and too opaque to be employed by jewellers. They are, however, 

 collected and exported to India, where they are calcined and formed into lime for the use 

 of wealthy betel chewers. They are also burned in the mouths of the dead. 



The shell is of great use in commerce, affording the substance from which is cut 

 those large flat " pearl " buttons that were formerly so fashionable, but .seem now to have 

 descended to th denizens of the stable. The button " moulds " are cut from the shell by 

 an instrument that somewhat resembles the trephine, by which portions of the skull are 

 removed in case of severe injuries, and in their rough state look like gun-wads. They 

 then pass through a series of processes in which they are polished and pierced, and made 

 ready for sale. 



THE lowest figure represents the SADDLE-SHELL, remarkable for the way iu which the 

 shell is attached to other substances. Two specimens may be seen in the illustration 

 placed on an oyster. The contrivance by which it is attached is most remarkable. The 

 animal deposits a plug or peg of shelly matter on the oyster, and in the right valve theil 

 is a hole or notch into which the peg fits, much after the fashion of a button. When the 

 left valve is in its place, this contrivance is hidden. The shell of this creature is 

 beautifully thin hardly thicker, indeed, than the paper on which this account is printed 

 and elegantly waved. It inhabits the British seas. 



THE three objects in the accompanying illustration represent different views of the 

 same species. 



The LIMA, or FILE-SHELL, is worthy of notice on account of the curious refuge which 

 it constructs by binding together a large mass of shells, corals, sand, and other materials, 

 by means of the silken threads or " byssus " which it is capable of secreting. On the 

 left hand is seen a specimen almost entirely buried in the mass of nullipores which it 

 has gathered around its shell. The upper figure on the right hand exhibits the same 

 shell as it appears when free and in the act of swimming. The long tentacular 

 appendages are kept in constant movement, possibly without the will of the animal, 

 keeping up 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. 



