Smaller and inferior pearls are found in a land¬locked bay on the north-east coast of Ceylon, known as Lake Tampalakamam. Here, upon a dark grey-black mud intermixed with quartose sand, is found the Placuna oyster, with valves which, during the first year of its existence, are so transparent that one can see its whole anatomy, even to the beating of its heart.

At two years of age the shells become more massive, and gradually turn white and translucent. At three years of age its size is about seven inches by six. The shell is used as a substitute for window glass. Placuna pearls are used in India for placing in the mouths of the dead at certain funeral rites, while in China they are reduced to powder and used as medicine.

In Ceylon the pearls are mostly secured by divers, who receive half the catch as their remuneration, but are obliged to open their oysters fresh and sell what pearls they contain, at whatever price the renter of the fishing rights chooses to pay. The diver makes from two to three hundred descents during the season, from about January to May, and he may secure daily from two to three thousand oysters.