15 
Year class* | Number % of total 
of shell. population: 
ls 28 18.8 
TIT. 63: 42.3 
IV. 44 30.2 
Vv. 13 8.7 
In this material it will be noted that shells belonging to the fifth year class 
are the oldest. In examinations of other material from this bed examples of 
shells in the sixth year class were found but their occurrence was very rare, so 
that they represent a negligible portion of the whole population. It will be 
seen also that the majority of the mussels of the bed belong to the third and 
fourth year classes, 7.e., are indiv duals that were spawned and settled in the bed 
while it was thinly populated and so had a good opportunity to develop. In 
Table IV. the above results are arranged to show when each season’s growth in 
the various year classes was made and the relative numbers of the various year 
classes in each year considered. 
TABLE IV. 
Showing relative numbers of each year class and when each season's growth of each year 
class was made in the mussel population of a typical bed at Biological Station St. Andrews, N.B., 
July 14, 1919. 
——— 
Relative Number of Mussels of Year Class 
Year 
1 II. III. IV. te Me VI. 
“1919 | Unknown 28 63 | dt | 13 | Negligible 
“ois | 28 | 63 44 13. | Negligible | 
“4917 | 63 44 13 Negligible | 
1916 | 44 ie 13 Negligable | F 
1915 is | Negligible 
“1014 Negligible 
pe ee ee eee ee eee 
The figures given in Table IV. are, of course, only approximately correct 
since they are based on an examination of a relatively small number of the 
mussels and since also they represent only the members of the various year classes 
which have survived up to July, 1919. They serve, however, to give some 
indication of the density of the population in preceding seasons and the relative 
numbers of the various year classes during those seasons. 
From these results it seems evident that the bed was destroyed possibly 
in 1914 and at least before the spawning season of 1915 and that only a small 
number of individuals spawned in 1914 survived. This deduction is supported 
by the condition of the beds in the region in 1917. As indicated in Section I. 
in that year the beds consisted of small mussels, the majority of which had a 
shell length ‘of between 2 centimeters and 3.5 centimeters. Moreover, mussels 
29 
