116 



MADRAS FISHERIES BULLETIN 



[VOL. XVI, 



mental equipment of the executive officer in charge of pearl bank 

 inspection if he be not a trained biologist. 



The Indian pearl oyster, Margaritifera vulgaris, is a small and 

 widely distributed species belonging to the large family Aviculidee, 

 which is closely related on the one hand to the Scallops (Pectinidse) 

 and on the other to the mussels (Mytilidse). All these exhibit a 

 number of primitive characteristics whereof the lining of the shell 

 in the case of the aviculids and mytilids with a lustrous pearly 

 layer — nacre — is one. 



Our local pearl oyster seldom exceeds 3 ! /2 inches in height and 

 slightly less than this in length. It is a typical bivalve mollusc, 

 and might with advantage be made a teaching type, so simple in 

 form and easily distinguished are the various organs. The shell 

 consists of a right and a left valve attached together along one side, 

 the hinge, by an elongated dark brown elastic pad, the ligament. 

 The hinge line is shallow at first, but with increasing age becomes 

 deep and gutter-like ; its depth and width are our best indications 





KlG. I. Indian pearl-oyster, Margaritifen vulgaris Schumacher. Natural size. 



of the age of the oyster. Each valve is roughly circular (sub- 

 quadrangular) with a tendency in the old to become slightly 

 oblong ; an ear-like projection (auricle) is given off at each end of 

 the hinge (fig. i). The two valves are somewhat asymmetric, the left 

 valve being deeper and more convex ; the margin of the right valve 

 is the more flexible, S3 that when the shell is tightly closed, the 



