160 Journ of the Asiat. Soc. of Bengal. [May & June, 1915. 
predatory starfishes, mainly the colour-variable Pentaceros 
nodosus ; Luidia maculata also abounds. 
aces where these mytilids do not monopolize the 
bottom the faunal diversity is greater. From 3 to 5 fathoms, 
abundant in these shallows, and in places a black Antedon’s 
seen in hundreds. Holothurians (H. atra and H. marmorata) 
are also characteristic, sometimes very common. 
age Why then, if such variety in species and such abundance — 
in individual numbers exist at a depth less than 5} fathoms, | 
are pearl oysters absent from these depths? It appears tom 
that the physical character of the bottom is not at fault; 1 
deed, from comparison with the known facts of the Gulf of 
favour. Neither is the planktonic food supply at fault in the. 
shallows, for I have always found greater abundance there 
the character of the bottom nor the food supply be at fault 9 | 
the shallower water, the absence of pearl oysters from 
area is most likely to be due to the presence of certain enemies 
there that are not found in the deeper water. Now nof@m | 
ceros nodosus were ever found on the pearl beds off Tondi, 
whereas these starfishes were often taken by the dozen in te 
dredge in depths below 5fathoms. Iam therefore forced tothe 
conclusion that the pearl oyster is able to thrive in depths of 
il 
