Did, 
gests the action of this factor, and if this be true, 1t becomes a tem- 
porary rather than an adventitious planktont. Temperatures seem 
to bear little relation to the occurrence of Oscillatoria in the plankton. 
Tetrapedia emarginata Schrod.*—Average number, 242,308. 
From the first of August till the end of October in numbers from 
1,000,000 to 3,500,000 per m.*, appearing later and in larger num- 
bers in October in 1897 than in 1898. At temperatures above 65°. 
Tetrapedia gothica Reinsch, Gleocapsa polydermatica Kutz., and 
Gleocapsa sp. were recorded once or twice in the midsummer plank- 
ton in relatively small numbers. 
CHLOROPHYCEA. 
(Plates I, and II.) 
Average number, 53,175,105, including, without duplication, 
species from both silk and filter-paper collections. In 1897 this 
was very much greater (139,739,850), owing to the prolonged low. 
water and higher temperatures of the late autumn. Although 
abundant, these organisms are outnumbered by the diatoms six to 
one, and by the synthetic Mastigophora by about two to one. The 
Chlorophycee of the plankton, with few exceptions, are minute, and 
generally escape through the silk net. Pediastrum and colonies of 
Botryococcus are about the only species of which the usual method 
of plankton collection in our waters affords a fair representation. 
The Chlorophycee appear in every collection examined through- 
out all the years of our operations, with the exception of eight in 
midwinter floods in 1895 and 1896. Asa group they are adapted to 
the whole range of temperatures, and exhibit in 1897, on April 28, 
a well-defined vernal pulse of 367,200,000, and a series of autumnal 
pulses culminating September 21 at 216,000,000, October 19 at 
367,200,200, and November 23 at 52,000,000. In this year the 
midsummer pulses are of minor importance in comparison with 
those of spring and autumn. In 1898 the vernal pulse is also well 
defined, culminating May 3 at 212,406,400, and it is followed by a 
series of four midsummer pulses of considerable magnitude, which 
culminate June 14 at 46,000,000, July 19 at 277,000,000, August 9 
at 370,000,000, and August 30 at 189,000,000. The autumnal pulse 
appears September 27, attaining 70,526,400. The summer and 
autumn hydrographs of this year are much more disturbed than in 
