IVes^ : Phytoplankton of English Lake District. 265 



Anahcena Lemmevmanni was observed during the warmest 

 period from June to September, and the development of the 

 spores took place from July to August. 



Peridinie^. The ubiquitous Ceratium hiviindineUa makes 

 its first appearance in May, increases considerably in June and 

 July, and is most abundant in August (temp. I2.7°C.), after 

 which it gradually diminishes until its complete disappearance 

 in the middle of December (consult text fig. 3). We have never 

 found it in any great quantity in any of the English lakes, and 

 it is always a seasonal plankton constituent with a summer 

 maximum. The same is true of the large pools of the Midlands 

 of England.''' In the more southern continental lakes, it is a 



Fig. 4. Peridiniiim Willei Huitfeldt-Kaas. A.-C, epivalve of three 

 individuals showing limits of variation in apical plates ; D., hypovalve ; 

 E. and F., ventral views of two individuals ; G., dorsal view. All x 500. 

 The areolations of the plates are not indicated in the figures. 



perennial constituent of the plankton, t but in the more northern 

 lakes of Germany, Denmark, Russia, and Scandinavia, it 

 completely disappears in the colder months, as in the British 



* G. S. West, ' A Biological Investigation of the Peridinieae of Sutton 

 Park, Warwickshire,' New Phytologist, 1909. 



t Brahm & Zederbauer, ' Beitrage zur Planktonuntersuchung alpiner 

 Seen, II.', Verhandl. k.k. Zool. — Botan. Ges. Wien, 1904: G. Entz, 

 * Beitrage Kenntniss des Plankton der Balatonsees,' Result, der wiss. 

 enforschung des Balatonsees, II. Bd. Budapest, 1904 ; Lemmermann 

 in ' Archiv. fiir Hydrobiol. u. Planktonkunde,' III., 1908, 



1909 July I 



