318 Birge—The Crustacea of the Plankton. 
winter of 1896-97 Aphanizomenon and Diatoma were present 
together; the latter form being more abundant at the opening 
of the winter and the former relatively increasing towards 
spring. Asterionella has been regularly present in all years as 
a small part of the summer plankton, but never has been predomi¬ 
nant except during a short time in the spring of 1897. Ceratium 
has been a leading alga in the summers of 1895 and 1896, but in 
1894 and 1897 there was no Ceratium period. Lyngbya predom¬ 
inated in July, 1895, but scattered filaments only were present 
during the succeeding two seasons, while in August and Sep¬ 
tember, 1897, it was again present in considerable numbers, 
though nowhere near as great as in 1894. The summer of 1895 
was definitely a diatom season, as was also that of 1897, very 
few of the Schizophyceae being present; while in 1896 the latter' 
plants predominated, although a considerable number of dia¬ 
toms were always present. In the autumn there has always 
been a diatom period, but the predominant forms have been 
Diatoma , Fragillaria , and Melosira in different seasons. The 
first alga to develop in the spring is one of those which has 
predominated during the winter, but the order of succession 
in the forms which follow is wholly uncertain, as the few illus¬ 
trations given above sufficiently indicate. 
LARGEST NUMBER OF CRUSTACEA PER CUBIC METER. 
The following list shows the largest number of Crustacea found, 
per cubic meter. It is computed on the assumption that the ani¬ 
mals are equally distributed through the three meter space cov¬ 
ered by each haul of the net and gives the average per cubic 
meter for the distance of three meters. In reality the maximum 
at the stratum of greatest abundance would be greater than the 
table shows. Probably 600,000 would not be too high as 
the maximum for the total number in a cubic meter. The 
numbers are given as thousands per cubic meter. All, except. 
D. pulicaria are from the upper, or 0-3 meter level. 
