139 
m.* on April 24, 1896, 2,287,160 on May 25, 1897, and the maximum 
record of all years, 5,247,800, on May 3, 1898. Pulses in excess of 
1,000,000 per m.* occur 14 times in our records: in July, August, 
November, and December in 1895; in April, 1896; in April, May, 
September, and October in 1897; and in May, June, August, Sep- 
tember, and October in 1898. There is, apparently, in years or 
seasons best represented in our records, a tendency for a vernal 
pulse, often the maximum one of the year, to occur in April-May, 
and for an autumnal pulse of large amplitude to appear between the 
last of August and the middle of October. The pulses contiguous 
to these major pulses of the year are often of considerable magnitude; 
as, for example, in 1897, when the maximum of September 7 (5,121,- 
000) is followed by another large pulse on October 12 (2,906,400), 
and in 1898, when the vernal pulse of May 3 (5,247,800) is followed 
by a June pulse, on the 21st, of large amplitude (2,601,200). The 
recurrent character of the pulses appears throughout maximum and 
minimum periods, and may be traced in Plates III. and IV. In the 
period of 15 months from July, 1895, to October, 1896, there are 10 
such pulses, and 6 months in which pulses do not appear. In the 21 
months from July, 1897, to March, 1899, there are 18 pulses, and 
3 months in which they do not occur. They often coincide with or 
approximate those of the Entomostraca (Pl. III. and IV.) and of the 
chlorophyll-bearing organisms (Pl. I. and IT.). 
With the exceptions of the November—December pulses of 1895 
at 33° (1,595,359 on November 27 and 1,636,640 on December 11) 
and the pulse of October 25 (1,048,620) at 48°, no pulse of con- 
siderable amplitude is found at temperatures much below 60° in 
channel waters. 
In the discussion which follows, 104 forms are listed, 6 belonging 
to the Rhtzota, 6 to the Bdelloida, 91 to the Ploima, and 1 to the 
Scirtopoda. 
RHIZOTA. 
The Riuzota by virtue of their fixed habit are represented in the 
plankton either by adventitious species, torn from their location on 
water plants or other aquatic substrata by disturbances in the water, 
or by colonial species with a free-swimming habit, such as Conochilus. 
As represented by the latter type they are of some quantitative im- 
