( 13 ) 
BULLETIN No, 2, 
STATISTICS DEALING WITH THE GROWTH RATE, &c., 
OF PLACUNA PLACENTA. 
By Joseph Pearson, D.tSc, F.R.S.E., F.L.S. 
Lj^OR the last ten years systematic measurements of Placuna 
-*- placenta have been made at Lake Tamblegam. In all 
over 13,000 oysters have been measured for weight, length of 
short diameter (hinge diameter), and length of long diameter 
and in the present paper the results of this work are 
summarized. These measurements were taken at the following 
inspections : — 
1912 
1913 
1914 
1915 
1916 
1917 
1918 
1919 
1920 
May, Jime, September. 
January, May, September. 
January, April, October. 
January, April, Julj^ September, December. 
March, August, September. 
January, May, September. 
Januarj', March, September. 
February, Jime-July, August. 
Janl^ary-Feb^ua^y, May, Octobei'. 
At these inspections oysters of all ages were examined, 
representing the following birth years : — 1909, 1910, 1911, 
1912, 1913, 1914, 1915, 1916, 1917, 1919, and 1920. 
So far as I am aWare this is the most complete series of 
measurements of a bivalve mollusc so far attempted, and the 
results are of sufficient interest to justify their being placed 
on record. Some of the more imj)ortant results of the work 
are the determination of (1) growth rate (linear) of Placuna 
'placenta up to the eighth year ; (2) the growth rate (weight) ; 
(3) the relation between the short and long diameters ; 
(4) the relation between the weight and linear measurement 
at all stages in the life history. 
