177 
Reports to the Colonial Office. 
beds. The crab is also said to be injurious, cutting the byssus of the 
oyster. A note is given on page 6 regarding an enemy that makes a 
round hole in the oyster shell ; this mysterious enemy is one of the 
carnivorous whelks. 
Evidently, from the report, numerous small mollusca prey on the pearl 
oysters. Two fish, the Trigger Fish ( Batistes mitis ) and skates ( Trygon 
warnalc), also do much harm. On page 5 it is stated that “ the numerous 
rock fish which abound on the Arippu banks feed on oysters . . . the quan- 
tity devoured by these voracious fish must be considerable.” Later, it is 
stated to be useful, as it preys on the injurious Suran or mussel. Skates of 
several unknown species are referred to as very destructive. Divers, both 
European and native, give various tales as to the damage done by sea 
snakes, but nothing authentic is given. 
Floods of fresh, muddy water are stated to be most injurious. 
Little definite seems to be recorded as to the age of pearl oysters, but 
it is stated “ that oysters may be profitably fished at the age of four years, 
and that they are in their prime at five years, and may be kept till that 
age if circumstances permit of it, but if they are kept until the sixth y ea 
they are almost certain to be found dead.” The best time to fish then: 
however, does not appear to be settled. 
The advisability of retaining native divers is entered into at some 
length, their superiority over the European at this work being clearly 
pointed out. Their reward is now raised to one-third of the oysters 
collected. Recommendations to start a chank fishery in the neighbour- 
hood of the pearl banks are given. One fishery exists north of Manaar 
Islands, about 2,000,000 chanks being exported from Jaffna to Calcutta. 
The chanks are used as ornaments by the Hindus. 
The main body of the report (39 pages) is taken up by eight appendices. 
The first dealing with spat, true and false ; enemies of the oyster ; chank 
fishery ; age of the pearl oyster and artificial culture ; being extracts from 
the report of Mr. Thomas, Madras Civil Service, to the Government of 
Madras, on the Pearl Banks and Fisheries of Tuticorin. 
The most important part in this report regarding the true spat is here 
reproduced : — 
“ The challenged spat in the largest shell which I have seen is 
4| sixteenths of an inch from hinge to contour rectangularly at its 
widest point, and the largest drawing in Sir J. Emerson Tennent’s 
work is no more ; it is, therefore, so small as to need very close 
examination. Looked at under a hand lens and under a low power 
microscope, I made it out to differ from the shell of the pearl oyster 
in being much more convex, more oblique ; in having the ear on the 
short side, not produced in an almost straight line, but rounded off 
and turned up instead of being flat ; in having the right valve fitting 
deeply into the left valve, with the edge of the right valve turned back at 
about an angle of 45° for the whole contour in some, for others only from 
the sinal ear to half way round the contour, instead of the two valves 
meeting each other nearly ffaf, as in the pearl oyster ; in having none of the 
spines with which the pearl oyster is covered, and distinctly different 
flanges ; in having no algce adhering to it ; in having the umbones more 
anterior or advanced beyond the hinge line ; in adhering to weed, said to 
be Saragossum vulgare, instead of to rock and such-like hard substances 
N 
