52 



So while the Ceylon bank is infinitely more fertile in the number of times it ia 

 replenished with oyster spat, its Indian counterpart has greater reliability ; six times 

 do we know that it has brought its oysters to fishing maturity, namely, in 17S4, 

 17S7, 1807, 1810, 1822 and 1889-1890, and very probably a third time" as well, for 

 the oysters noted in 1SG0 as 3| years old were in all probability there iu lS'U, in the 

 spring of which no examination was made, the officers in charge being busy with the 

 fishing of oysters of a similar age on the inshore pars. This divergence in results is 

 due in great part to the Ceylon bank being situated in a relatively more exposed 

 position being close to the edge of the precipitous submarine cliff that margins the 

 seaward aspect of the Ceylon Pearl Bank plateau. As a consequence the heavy seas 

 which characterise the period of the south-west monsoon break iu unmitigated 

 violence upon the Periya Par, whereas on the Indian coast the movement of the 

 water during the same season has undergone considerable amelioration when it reaches 

 the Tolayiram Far from travelling over a couple of hundred miles of comparatively 

 shallow water. 



Faunistic and many physical (chiefly geological) characteristics link the Tola- 

 yiram with the Periya Par; but in regard to the aspect and degree in which the 

 former meets the fury of the south-west monsoon, its position is more comparable 

 with that of the Cheval Par which lies on the leeward side of the Periya Par, and 

 is as consistently reliable as the latter is the converse. 



The value of the Tolayiram Par may be assessed as midway between the Cheval 

 Par and the Periya Par, inferior to the latter chiefly by reasou of oyster spat being 

 less abundant and to current conditions (surface-drift) being less favourable to the 

 deposit of such spat on the Indian than the Ceylon side ; — partly also to the conditions 

 of life being somewhat less favourable on the Tolayiram Par owing to the greater 

 amount of sediment present in the sea on the Indian side. 



The data for the institution of comparison between the rate of growth normally 

 characteristic of the Tolayiram Par oysters with that of oysters from typical localities 

 on the Ceylon side rests upon a single series of measurements and weights of that 

 generation of the former that survived to a fishable age in 1889. The resultant 

 comparisons based upon these dimensions are highly dnstructive and while in my 

 opinion I believe it is probable that they are quite typical of the normal progress of 

 growth of oysters on this par, further series of growth observations are desirable and 

 Inspectors after this should be instructed to record the necessary particulars on every 

 available opportunity. 



Two methods of "comparison are available : (a) the external dimensions of the 

 oysters when alive, and (b) the weight of the cleaned shells. 



Making use of the former method we find usually but little increase in the length 

 and depth of the shell after the third year ; the shell secreting energy of the animals 

 being thereafter occupied chiefly in adding to the thickness of the valves. 



I now attach greater importance to observations upon the average weight of 

 oyster shells than upon measurements of length and depth, increa.se being nearly as 

 steadily progressive in old age in the case of weight of shell as it is during the first 

 three years of existence ; it furnishes us with the most reliable guide available in the 

 assessment of age that I know of. 



But we need to have considerable knowledge of the special growth peculiarities 

 of the ground we deal with. Some pars by reason of abundant food supply hasten 

 the growth of their oysters to a surprising degree, while others where less favourable 

 conditions prevail bear oysters of an unhealthy appearance and of stunted size. 



Cn the Ceylon side two distinct types of oysters are found, the one large and 

 vigorous, peculiar to the Southern and Eastern Cheval and Moderagam Pars, the 

 other slow-growing, small and stunted, characteristic of the rocky banks of the 

 Muttuvaratu, Mid- West and North- West Cheval. 



We will now proceed to compare the sizes and weights of the generation of 

 oysters carefully guarded on the Tolayiram Par by Captain Phipps from 1884 to 

 1889 with those of oysters of the two types referred to on the Ceylon side. 



