274 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
that the fluctuations in the summer of 1907 may have 
been due to some unknown factor or some unnoticed 
irregularity in the conditions. 
The relatively high figure of the average catch for 
May this year (61°18), as compared with that of April 
(63°35), is clearly not due to phyto-plankton, as although 
the Dinoflagellates have increased to some extent, the 
enormously more abundant Diatoms have been 
diminished by about one-half (less than six millions as 
against eleven and a half). Some other more bulky 
organisms (such as Sagitta and the smaller Medusz) 
have brought up unduly the average volume of the 
catch for May. 
ANNUAL POSITION OF CHIEF MAXIMA. 
We showed in last year’s report that the three 
important groups of organisms—Diatoms, Dinoflagellates 
and Copepoda—had their vernal or summer maxima in 
a definite order of succession in all the three years 
(1907-09) there dealt with. When the curves are put 
together on the same sheet, the Diatoms occupy an 
earlier and the Copepoda a later position, while the 
Dinoflagellates le between. We have now to add that 
in 1910 the chief maxima again occur in the same 
order—the Diatoms are most abundant in April and in 
June, the Dinoflagellates in July, and the Copepoda from 
July on to September. 
THe More ImMporTANT GENERA OF DIATOMS. 
We add this year a seventh genus, Lauderia, to the 
six dealt with in our last report. This we do because 
the single species Lauderia borealis is of marked 
importance this year, running as it does to numbers over 
a million per haul on several occasions in April and 
