THE MICROPLANKTON OF PLYMOUTH SOUND. 153 
THE PERIDINIALES. 
In the microplankton the group of Peridiniales comes next to the 
diatoms in importance. A very large number of these go through the 
finest net, and practically all the smaller forms including almost the 
whole of the Gymnodiniacee are lost. Former tow-net records show hardly 
any of these. Ceratiwm and the larger Peridinium species have been 
shown to be plentiful, but there is a very marked absence of the smaller 
1400 : 
1000 
900 i" 
PERIDINIA LES 
800 | | 
700 
400; — easels ee Tt —= 
| | | | | 
! | 
SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY AUG, SEPT. 
1915 1916 
Fie, §.—Curve showing the average number of Peridiniales in 1000 ce. for each month. 
0 
forms. This is perhaps the group which shows the loss from the net to 
the greatest degree. Because of the number of new species and new 
records of this group I have given the systematic details in a separate 
paper of this journal (p. 183). Lohmann has described many new 
forms from the microplankton, and several of these are found to occur 
here. In most cases his numbers are much greater than mine ; also the 
numbers given in Prof. Herdman’s records for Port Erin are very large, 
but the different methods employed make the two records hardly com- 
