134 



SPOLIA ZEYLANICA. 



Date. Observations. 



March, 1908 . . Average of 22 : 181 by 165 mm. These 



are large scattered individuals living 

 under conditions favoui-able to growth ; 

 and the apparent average increase of 

 size since October may depend as much 

 upon individual variation as upon the 

 general growth of the colony ; about 

 4 years old. 



Table III. — Kakkaimunai. 



The Kakkaimunai oysters are in general dwarfed and of unequal 

 growth, hence the averages are only approximately comparable. The 

 observations indicate that this bed is a favourable spot for the settle- 

 ment and rapid, though limited and stunted, growth of Placuna. The 

 oysters are crowded side by side, thus prejudicing their bodily 

 growth, and perhaps also their total pearl productivity, but not 

 affecting their sexual maturity ; hence the Kakkaimunai bed acts as 

 a natural reserve. 



May, 1905 (Hornell) 



Jime, 1907 



October, 1907 



March, 1908 

 Do. 



Of two samples, one estimated at 1|^ year 

 old gave an average size of 1 11 • 4 by 

 102 mm. ; the other estimated at 1| 

 year old gave an average of 125 "2 by 

 114 "96 mm. Combming these two 

 sets we obtain an average of 118' 3 by 

 108-48 mm. 



Average of 12 specimens: 119 -.3 by 111 

 mm. It seems certain that these 

 oysters belong to the same generation 

 as those seen by Mr. Hornell in 1905. 

 It would follow, therefore, that there 

 had been practically no growth in 

 superficial area, but only in the thick- 

 ness of the shell. 



Average of first sample of 30 (October 17), 

 131-5 by 123-5 mm. A total of 79 

 oysters was measured on this date : 

 the smallest 106-25 by 92-75 mm.; the 

 largest 159-4 by 146-9 mm. This is 

 an extreme variation tending to vitiate 

 the average. Second sample of 30 

 (October 22) : 135 by 124-25 mm. 



Average of 16 toi^otypes : 129-2 by 122- 1 

 mm. This is nearly identical with the 

 average of the October topotypes. 



Average of 16 plants {i.e., oysters trans- 

 planted in October, 1907, from Kakkai- 

 munai to Nachchikkuda) : 141-8 by 

 130-1 mm. 



Table IV. — Sembian-aar. 



It will be noticed that while the oysters on this bed show a larger 

 growth than those on the Kakkaimunai bed, yet they resemble the 

 latter in having made little increase in size since 1905. 



May, 1905 (Hornell) . . This bed " was particularly prolific in 



fine, well-grown oysters from 10 to 16 

 to a dive." Average size : 155 by 

 142*25 mm. (6g by 5f inches) ; " prob- 

 ably over 2 years old." 



