54: Proceedings of the Royal Irish Academy. 



December. Staurastrum is also present iu Dncli Earn, but is absent from 

 Loch Lubnaig. 



In the Baltic lakes only a few species of Staurastrum occur, and they 

 never attain great abundance. S. paradoxum is not recorded by Kofoid, but 

 S. gracile was present in the waters of the Illinois iu small numljers fi-om 

 March to January, with a maximum of 14,000 in September. 



Sphaerocystis. 



SpJuteroeysti-s SJuoeteri Chodat. — This species occui's in the plankton of 

 Lough Neagh more frequently than any other member of the PalmeUaeeae 

 or the Protocoecaceae, although it is not very abundant.* From November 

 to February it is absent. In March it occurs in small quantities, and 

 increases rapidly until in May it reaches a maximum of 121,000 colonies in 

 the bottom-to-surface catch. 



Messi-s. West record S. Schroeteri from Ennerdale Water, where it reaches 

 its maximum in Jime. It diffei-s from the same species iu Lough Neagh by 

 being absent in August, but present in very smaU quantities dm-ing the winter 

 months, whereas in Lough Neagh it is fairly abundant in that month, and 

 absent in the winter months. In Wastwater it reaches its maximum in 

 October and November, while in Loch Lomond it occurs most abundantly in 

 July, August, September, and October. In Loch Katrine it is always very 

 rare. The same is true of Loch Earn, while it is absent altogether from Loch 

 Lubnaig. 



Wesenberg Lund records S. Schroeteri from some of the Danish lakes. It 

 appears in May, has its maximum in June, and disappears in August to 

 September. Apstein does not record S. Schroeteri from the Baltic lakes. 



It is one of the main forms of the Euehlorophyceae occurring in the 

 arctic freshwater plankton. In the north European lakes Sphaerocystis 

 Schroeteri is the most abxmdant of the Chlorophyceae. In the Baltic lakes 

 S. Schroeteri is much less common ; while in the centi-al Em-opean alpine lakes 

 it occurs in still smaller quantities. 



DietyosphaeriunL. 



D.pulchellum Wood occurs in the plankton of Lough Neagh in very small 

 quantities. Its maximum is probably in August-September, although it 

 occurred in fair quantities in February. It was absent again from October 

 to January and from May to July. 



Zilessrs. West record it from Ennerdale Water, where it reaches its 

 maximum in August and September. It also occui-s fairly commonly in 



