SEA-FISHERIES LABORATORY. 985 
Biddul- Chaeto- Coscino- Rhizo- Thalas- 
Date. phia. ceros. discus. solenia. siosira. 
Oct. 20"... 525 1,500 62 50 0 
flay ee eae 112 550 50 12 0 
Aa ee 150 1,172 62 25 0 
HmaGrees 325 1,775 237 12 0 
Sets Pepe 365 3,895 260 15 ) 
ito? 4. 280 2,455 505 50 0 
INOv.« 2... 1,090 3,050 645 15 0 
1. ae 1,750 2,405 91>” 105 0 
EMAL Osc 1,620 435 840 65 0 
“eB ae 3,375 2,762 612 37 0 
“pede arae 2,185 715 530 0 0 
Mee. 4 ... 4,190 2,630 955 15 0 
PSLGr ava 1,990 500 415 0 0 
RGN Ie: kas 3,300 425 880 i) 0 
eae) (Cc: ) 5,000 200 500 0 ) 
In comparing curves drawn from these lists, it is 
found that the curve for the total Diatoms in the bay 
from January to April practically agrees with the curves 
of Biddulphia and Coscinodiscus, and these two agree 
with one another. From April 20th onwards the maxima 
are caused in turn by Chaetoceros debile on April 29th, by 
C. sociale in May, by C. socrale and C. teres and Ahizo- 
solenia in early June, and by Rhizosolenia and Gwinardia 
flaccida in late June and early July. The maxima in 
total plankton catch coincide with the above-noted Diatom 
maxima, with the exception of that on June 10th, 
apparently caused by Mvadne and Copepoda. Biddulphia 
and Coscinodiscus influence the value of the total catch 
apparently far more, in proportion to their actual 
numbers, than do Chaetoceros and Rhizosolenia. This is 
no doubt due to their larger size individually. 
Tt will be noticed that the maximum for Biddulphia 
and for Coscinodiscus is about the middle of April, for 
Chaetoceros late in May, and for Rhizosolenia at the end 
of June. The minima also differ, Brddulphia being 
practically absent when Chaetoceros and Rhizosolenia are 
present in greatest abundance. 
In considering how the chief elevations in the Diatom 
