TEE I'LACUXJ.. 235 



water, for if the frost catches them it nips them up. Particularly dangerous are also the floods 

 from melted snow, and as fresh river water alone is sufficient to kill Oysters, much more so are 

 they in danger if the temperature is reduced by melting ice or snow. Valuable layings of Oysters 

 have thus been frequently destroyed by winter floods too powerful for the flowing tide to dilute. 

 This great abhorrence of cold on the part of high-bred Oysters, such as natives, is, in my 

 opinion, one of the principal causes of their high price. Of late years the summers have been 

 very cold, and although the water may perchance have attained to a certain amount of heat, 

 yet the cold nights knock all the warmth out of it again. Above all, it is necessary for a fall of spat 

 that the temperature should not jump up and down, but be as equable as possible, 'Ihe young 

 Oysters cannot help being born, and when born they must take their chance of the weather. If it is 

 cold, they die ; if it is warm, and they are lucky enough to find cradles in the form of ' culch ' suited 

 for them, they hold on as tight as barnacles, and have a chance of living." 



Many British cists and cairns have disclosed relics in the form of shell necklaces and bracelets 

 made of the Oyster, Limpet, and Cockle-shells, the contents of which supplied an important source of 

 food. For not only in the ancient kitchen middens of Northern Europe, but mingling with more 

 ancient cave deposits, as in Kent's Cavern, lay heaps of the shells of such edible Molluscs, the refuse 

 of the repasts of the old cave-men, which show one resource on which they depended for sub- 

 sistence. America, too, had its ancient shell and refuse heaps, as at Cannon's Point, St. Simon's 

 Island, Georgia, where vast mounds of Oyster and Mussel shells, intermingled here and there witli 

 a Modiola or Helix, and with flint arrow-heads, stone axes, and fragments of pottery, cover an 

 area of not less than ten acres. They also abound upon all the sea islands of the Southern 

 States, and in many cases constitute regular sepulchral mounds or shell cairns. One of these 

 singular cairns on Halling's Island, in the Savannah River, more than two hundred miles from its 

 mouth, is an elliptical mound, measuring nearly three hundred feet in length, and enclosing human 

 skeletons, ike. On the islands, and along the coasts of Georgia and Florida, the inexhaustible supplies 

 cf Oysters, Conches, and Clams furnish abundant food. Around all the Indian villages these shells 

 may be observed accumulated in vast heaps ; and even now at places they show the circular 

 hollow where the native hut once stood. 



FAMILY II. ANOMIAD2E. 



Genus Anomia.* The shells of Anomia are very variable in form, being nearly always attached 

 to the surface of shells of other Mollusca, the pattern of whose markings they mould themselves to. 

 The shell is translucent, nearly round, and attached by a plug passing through a hole or notch in the 

 right valve ; the lower valve is concave, the upper valve convex, and the muscular impression sino-le,- 

 Twenty species are found living. They are not edible. They occur from low water to 100 fathoms. 



Genus Placuna,^ "Window-shell." The valves of Placuna are nearly round and almost flat; 

 the hinge cartilage is fixed by two ridges on the right valve, with corresponding grooves on the left ; 

 the muscular impression is double ; there are one large round scar, and a smaller, crescent-shaped, 

 in front; the shell is pearly and translucent. Four species are living in India, Australia, China, 

 and Ceylon. 



" The Tamblegam Lake produces in singular perfection the thin transparent Oyster (Placuna 

 placenta), whose clear white shells are used in China and elsewhere as a substitute for window-glass. 

 They are also collected annually for the sake of the diminutive pearls contained in them. These 

 are exported to the coast of India, to be calcined for lime, which the luxurious affect to chew with 

 their betel. These pearls are also burned in the mouths of the dead. So prolific are the Mollusca of 

 the Placuna, that the quantity of shells taken by the licensed renter in the three years prior to 

 1858 could not have been less than eighteen millions. They delight in brackish water; and on 

 more than one occasion an excess of either salt water or fresh has proved fatal to great numbers 

 of them."* 



The pearl fishery of Lake Tamblegam, near Trincomalee, clears 300 a year ; individual pearls 

 of P. placenta do not exceed 6s. in value. 



* Greek, anomios, unequal. + Greek, plakous, a thin cake. 



I Sir J. Emerson Tennent : "Ceylon," vol. ii., p. 492. 



