Dakin and Latarche— 7%e Plankton of Lough Neagh. 37 



1910. 



Nov. 11, . Sun and clouds. Previous weather cloudy. Sea calm. 



Wind light S. Eain and very rough weather for previous 



fortnight. Surface temp. 7"5°C. 

 Dec. 2, . Bright sun. Clouds. Strong east wind. Sea variable (wind 



off land). Frost on previous days. Surface temp. 5-0^ C. 



1911. 



Jan. 12, . Sun at intervals. Wind S.W. Some rain. Sea moderate. 



Surface temp. 4'6°C. 

 Febr. 3, . Bright sun. Sea calm. ISTo wind. Surface temp. 5-0° C. 



DISCUSSION OF INDIVIDUAL SPECIES PEESENT IN THE 

 PLANKTON OF LOUGH NEAGH. 



PHYTOPLANKTON. 



The species of algae occurring in the plankton of Lough Neagh are as 

 follows : — 



Tabellaria. 



Tabellariafenestrata var. asterionelloides Grunw. — Tabellaria is undoubtedly 

 our most characteristic plankton organism. It occurs in prodigious quantities, 

 and is easily first on the year's catches. At times the plankton is almost 

 entirely composed of this form. Another extremely interesting point is that 

 Tabellaria feiiestrata always occurs in the " star" colonies. One or two very 

 isolated chains have been found in the millions of stars. These results differ 

 greatly from those observations on the lakes of Denmark, where Tabellaria 

 is rare everywhere as a plankton organism, and occurs both in chains and 

 in stars. 



In Ennerdale Water in the English Lake District the star-shaped form of 

 colony is practically absent ; in Wastwater it is entirely absent. In Lough 

 Lomond, which, so far as Asterionella is concerned, presents some agreement 

 with Lough Neagh, we find Tabellaria occurring more frequently. West's 

 data do not allow of a comparison so far as numbers are concerned, but there 

 is nothing to show that Tabellaria var. asterionelloides ever attains the position 

 which it occupies in August in Lough Neagh ; and we never find the chain 

 form which is present in Loch Lomond. 



Moreover, Coelosphaerium is the dominant form in Lough Lomond when 

 Tabellaria is at its maximum. This is not the case in Lough Neagh. In 

 Lough Neagh the number of Tabellaria present drops after August ; but it 

 remains quite common all the year round, and though a minimum occurs in 



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