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MADRAS FISHERIES BULLETIN 



VOL. XIV, 



into a short " ear, " a modification of the wing-like projection that 

 gives the Aviculids proper their name of " wing shells." Ventrally 

 the shell is deep and rounded with a series of finger-like projections 

 at the ends of radial lines made up of older fingers now outgrown, 

 worn, and disused. These pearl-oysters reach their limit of size in 

 about 3^^ years ; if they live longer the shells become worn, the 

 fingers disappear and the over-all length and depth sometimes 

 actually decrease ; the thickness increases until death and this 

 then is our best criterion in determining the age of pearl-oysters. 



Flc. 39 The Indian Pearl-oysler {Mart:aritif,ra z-i/Ix'an's). 



Natural size. 



Pearl-oysters in life-history and habits are akin to the mussels. 

 A strong cable of byssal threads attaches them to rocks, stones 

 and other shells ; they possess the power of cutting their cable or 

 rather of casting it off, at will ; they are capable of crawling short 

 distances and this power to shift their foothold sometimes enables 

 them to avoid entombment and death through an overwash of sand. 

 When quite young they are restless and inclined to shift their 

 position frequentl3^ I have often seen them do so six or seven 

 times within a few hours, each place of attachment marked by a tiny 

 tuft of golden byssal threads. The formation of one of the threads 

 forming the byssus takes only a few seconds; the thread is formed 



