18 PEARLS [CH. Ill 



The oyster of Ceylon belongs to a group of 

 molluscs known popularly as bivalves, but more 

 scientifically as Lamellibranchiata. This name re- 

 fers to the characteristic plate-like gills. The group 

 includes the well-known edible oyster, the edible 

 mussel, cockle, and almost all the other shellfish 

 which produce pearls. The Ceylon pearl oyster is 

 a near ally of the scallop, a lamellibranch caught 

 in large quantities at many places round the British 

 Islands and enjoyed as a luxury by the few who have 

 recognised its delicate flavour. The degree of re- 

 lationship between the scallops and the Ceylon pearl 

 oyster is, as a matter of fact, much closer than that 

 between the latter and our edible oyster. 



The soft body of the animal is enclosed between 

 two valves of shell which are hinged together along 

 a line which is dorsal in relation to the body. The 

 opposite edges of the valves, at the shell opening, are 

 therefore ventral and each valve is situated laterally 

 on the creature's body — that is, there is a right and 

 a left valve. 



Each valve is rounded in outline, but the dorsal 

 edge or hinge is flattened and ends in wings (or 

 auricles) in front and behind. 



The shell of a four-year-old oyster measures 

 about 9*0 cm. from the hinge-line to the opposite 

 ventral edge and about 8*5 cm. across the valves. 

 The shell is not thick like that of the edible oyster or 



