the Pearl Oyster and on the Production of Pearls, 89 



the case referred to by Mobius of a worthy Hamburgher, whose 

 tongue deteeted the presence, in an oyster which he was on the 

 point of swallowing, of a pearl, for which a jeweller paid him 

 upwards of three pounds (22 dollars). The common Anodonta 

 cygnetty L., of our fresh waters, also occasionally contains small 

 pearls; and the European Pearl Mussel {Unto margaritifer, L.) 

 is the object of considerable fisheries in some parts of Germany, 

 as it was formerly in our own country. Of other known pearl- 

 bearing Mollusca, Dr. Mobius mentions that the Pinna nobilis, L., 

 produces a brown pearl; Mytilus edulis, L., a pale-blue one; 

 Spondylus gcederopus, L., greenish and pale rose-coloured pearls ; 

 Area NocE, L., a violet, and Anomia Cepa, L., a purple pearl. 

 Nearly allied to the latter is the species referred to by Dr. Ke- 

 laart as the Tamblegam Pearl Oyster (the Placuna placenta, L.), 

 which, like the Anomia, belongs to the great family of the Os- 

 treidce. It is found in the salt-water lake of Tamblegam, which 

 is separated by a narrow neck of land from the great harbour of 

 Trincomalee, and although the pearls produced by it (which are 

 of a lead-colour according to Mobius), are not more than one-third 

 of the value of those obtained from the true Pearl Oyster ; still, 

 as the number of pearls procured from them per thousand is three 

 times as great as that obtained from the Meleagrina, and the 

 shells, according to Dr. Kelaart, are worth at least ten shillings 

 per thousand, whilst those of the true Pearl Oyster of Ceylon 

 are of little or no value in consequence of their small size, there 

 seems to be every reason for believing that, with proper manage- 

 ment, this pearl-fishery of Tamblegam would constitute an im- 

 portant source of revenue to the Government of Ceylon. This, 

 however, as we shall see, is at present by no means the case. 



The Tamblegam Oyster (Placuna placenta) is called the ' Vitre 

 Chinoise' by some French writers, and the 'Window Oyster' by 

 English travellers in China, from the circumstance that its semi- 

 transparent shells are used by the Chinese instead of glass in 

 windows. "When full grown, the valves measure, at their 

 broadest transverse diameter, from 6 to 7 inches, and their 

 longest longitudinal diameter is about the same ; some, half an 

 inch more." They appear to arrive at maturity in about three 

 years, and to thrive best in brackish water, although they are 

 destroyed by a great influx of fresh water. As in the true Pearl 

 Oyster, the young have ova in their ovaries. The Tamblegam 

 Oyster, "having no byssus, is not attached to any hard sub- 

 stance, nor is it cemented, like some of the edible oysters, by 

 the hinge, or by one of the valves, to any object, but lies either 

 flat on the mud, or is fixed loosely in a semi-vertical position, 

 with the wedge-shaped hinge buried in the mud." From this 

 circumstance, coupled with the exceedingly flattened form of 



