88 
in the December plankton of 1894, but was exterminated from the 
channel plankton taken in the following February by the stagna- 
tion attending the long-continued ice blockade. It reappears in 
April, and again disappears promptly, but does not return until 
September 12, and not in numbers until October. There are pulses 
November 20 (506,800) at 42.8°, and December 30 (362,520) at 36.5°. 
The December pulse is followed by a decline, with a rise during 
February to a well-sustained maximum during March, approaching 
400,000, and at from 35° to 48°. The decline follows in April, and 
there are only isolated occurrences in small numbers at irregular 
intervals during the summer. Continuous occurrence begins again 
in September, and numbers rise rapidly in October. There is a pulse 
of 542,699 on December 3 at 32.2°, and another on March 22, 1897, 
of 159,500 at 43.8°. Synura is very rare indeed in the summer of 
1897, and in the prolonged low water, sewage contamination, and 
higher temperatures of the unusual autumn of that year it does 
not reappear continuously until October 26, at 59°, and does not 
exceed 1,000 until December 7, at 32°. There is a low maximum 
of 98,700 on December 14 at 36°, followed by a decline during the 
rising flood of January—March, 1898. The slight cessations in the 
flood invasion (Pt. I., Pl. XII.) in January and in the second weeks 
of February and March produce prompt responses in immediate 
rise in numbers in Synura. Finally, a low maximum of 320,600 is 
attained upon the crest of the March flood, on the 29th, at 49°. 
This is followed by a decline during April and a few scattered 
appearances during the summer. Synura returns at the end of 
October and rapidly mounts to a pulse of 1,999,500 on November 
29 at 35° with the first decline of the November overflow (Pt. L., 
Pl. XII.). A second pulse of 2,764,800 on December 20 at 33°, 
under the ice, gives way to a decline to 51,600 towards the end of 
January, 1899, during rising water. On February 14 another pulse 
(348,800) appears at 32.5°, under heavy ice, and declines agaim in 
the sudden flood of the last days of February, but recovers quickly 
with a maximum pulse of 898,800 on March 7 at 32.8°. Within a 
fortnight this falls to the low level of 9,800, but its further history 
was not followed. 
From these data it is evident that in our waters at least Synura 
is limited to the months from October to April, except isolated and 
irregular occurrences of small numbers during the summer. Its 
