No. 6 (1921) COMMON MOLLUSCS OF SOUTH INDIA 



155 



The best known Indian species are Area granosa, Area tortuosa, 

 Barbatia barhata, Peetuiieuhis taylori and some small species that 

 live in crevices in corals. 



The Ribbed Ark-shell, Area granosa {vari matti, Tamil), is 

 a fine shell found widely but sparingly distributed on the East 

 Coast in backwaters and estuaries. Nowhere is it common. In 

 appearance it looks like a very rugose cockle; the tlesh is dis- 

 tinctively coloured red, due to the blood being of this hue, an 

 exceptional condition among molluscs where the blood is generally 

 colourless or tinted pale bluish-green. The flesh is tough, but 

 because, presumably, of its red colour, some shore dwellers have 

 the idea that it has specially nutritious and strengthening quali- 

 ties ; on this account it is often given to women during pregnancy. 

 In size it seldom exceeds 53 mm. in length by a thickness of 

 43 mm. 



It is noteworthy that this species is the subject of very profita- 

 ble cultivation in Japan, where from a culture area of 830 acres 

 between 75,000 and 100,000 bushels have been obtained annually. 

 The method employed is simple ; it depends for success upon the 

 fact that the fry of Area, after quitting the free-swimming stage, 

 tend to settle in definite areas in great quantities. Once these are 

 discovered the young ark shells can be raked up in thousands, 

 usually when they are about 3 mm. long, and transplanted to 

 culture grounds where they are strewn and left to burrow into the 

 bottom. As they grow larger, from time to time they are redistri- 

 buted in order that overcrowding and food shortage may be 



avoided. They are said 

 to attain a marketable 

 size in their third year. 

 The bulk of the produce 

 is exported to China. 



In the open sea, 

 particularly in Palk Bay, 

 the estuarine Area 

 grajwsa is replaced by 

 the Hairy Ark-shell 



Fig. 37. The Twisted Ark-shell, X i. 



{Barbatia barbata) and the Twisted Ark-shell, Area {Parallelopipedum) 

 tortuosa. The former is ribbed and cockle-shaped, covered with a 

 dense black periostracum thickly beset with short black bristle-like 



