No. 6 (1921) COMMON MOLLUSCS OF SOUTH INDIA 177 



in the beds of sea grass along the south side of Palk Bay, and 

 bathers there must beware of the knife-like edges of its posterior 

 margin standing erect out of the sand a couple of inches or more. 

 Pearl oysters sometimes settle in numbers on these projecting 

 edges; in the 1905 Ceylon fishery when some millions were fished 

 from such foothold, the divers complained bitterly of the injuries 

 they received in pulling the Pinnas out of the sand; as many as a 

 dozen oysters sometimes clung to one Pinna — the reason being 

 that this area was almost all sand and the projecting shells of 

 Pinna were the only stable objects to which the oysters could 

 cling. 



Pinna has a tongue-shaped foot and spins a strong byssus of 

 very fine silky green fibres, wholly unlike the coarse strands of the 

 byssus of the pearl oyster. Occasionally thread has been spun 

 from these fibres and silky gloves and stockings woven therewith, 

 but these are mere curiosities and have no commercial importance, 



A second species, shorter and stouter, the SMOKY PiNNA {Pinna 

 fumata) is common in 5 fathoms in Palk Bay. 



No one eats Pinna on the Indian Coasts but in China it is in 

 great demand; in Japan great numbers of the large adductor 

 muscle, circular discs of white flesh measuring 1Y2 to 1^/4. inch in 

 diameter are cut out and dried for export to China, in similar way 

 to the treatment of the foot of the Ear-shell {Haliotis). 



The False Cockles {Carditidac) are often uncommonly like the 

 ordinary English cockle, thick and heart-shaped and deeply ribbed 

 with radiating ridges. Typical of this form is Cardita hicolor, a 

 coarsely ribbed species unevenly spotted v\ ith daik red on a ground 

 rendered yellowish by thick periostracum. It is common on coarse 

 sandy or even gravelly bottom. Like the cockle the foot is sickle- 

 shaped, and highly muscular ; by its aid these molluscs are able to 

 hop along the bottom. 



A circular outline and a pure white shell are features very 

 general in the Lucinidae. The form of the anterior muscle scar is 

 still more characteristic ; it is of unusual length and for the most 

 part lies separate a little distance within the pallial line. Liicina 

 cummingi is typical, with a long vermiform foot longer than the 

 length of the body, specially useful in burrowing in the loose sand 

 where it is found en both our coasts. More conspicuous is the fine 

 Bladder-shell. Cryptodon vesicnla, a thin fragile wb'te shell almost 

 globular in form. Unlike i.»a;/<:7, which has a toothed hinge, in the 

 II 



