THE PEARL FISHERY OF 1904. 27 



was it with the inroads of the boring sponge, Cliona ma/rgwitiferce, already alluded 

 to. Hundreds of valves were examined where not only was the substance of the 

 shell riddled by its honeycomb-like tunnels (see fig. 9), but, a more serious matter, the 



Fig. 9. Pearl-oyster shell honeycombed by Cliona inargaritifine, Dendy. 



insertion scar of the adductor muscle was tuberculated and diseased, a condition due 

 to the inferior powers of nacre-production of the epidermal layer in this region. " So 

 great indeed was the nacreous tuberculation in some cases, that I have seen the natives 

 save these shells with a view to cutting the tubercles off to use in the manufacture of 

 native pearl jewellery." Whenever the inroads of Cliona were extensive, the 

 sub-epidermal tissue in particular, and the other tissues in general, were thin and 

 diseased-looking. A fairly large proportion of the dead shells found during the 

 fishery on the South-west Cheval was badly affected ; Cliona must undoubtedly be 

 included among the more destructive agencies with which we have to contend. 



" There was no evidence of any depredations on the part of Ray fishes this 

 year, like the destruction of the Periya Paar Kerrai oysters last year. Rays were, 

 however, several times seen ; on the 27th February a large shoal, heading south, 

 passed the ship at anchor on the North-west Cheval. The sight was a remarkable 

 one, the sea for over 20 yards square being one patchwork of yellow disk-like bodies. 

 Fair-sized exan^les of Trygon walga were caught from time to time. None of them 

 furnished direct incriminating evidence, the stomachs being filled with crustacean 

 debris and fragments of lainellibranch shells other than those of the pearl oyster. 

 Like the trigger fishes, these smaller rays would appear to find the present size and 

 strength of the oysters too great for the power of their teeth and jaws." 



No sharks were seen on the fishing grounds. Mr. HoRNELL says : " During all the 

 months I have spent upon the pearl banks during the last 2^ years, I have 



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