Dakin and Latarche — The Plankton of Lough Neagh. 47 



absent from the lakes investigated in the lake district in their research on the 

 seasonal changes (Linn. Soc, Jour., 1912). Gomphosphaeria lacustris is 

 however, present. Wesenberg Lund records this alga as being rare in April 

 and May and reaching its maximum in autumn. 



C. Naegelianum has been recorded from Eussian Lapland, and so occurs in 

 the Arctic lakes. It is remarkably common in many Central European and 

 Baltic lakes. The species is recorded from certain of the alpine lakes — Katzen 

 See, Zurich See, etc. Coelosphaerium is stated to be absent from the 

 African lakes. 



On the. whole, Loch Lomond seems to resemble Lough Neagh so far as 

 Coelosphaerium is concerned more than any other lake, for which we have 

 details, in the British Isles. There, for example, we find C. Kutzingianum 

 almost all the year round and attaining a maximum in September-November, 

 with low period in December-January. Messrs. West state that it occurs in 

 slightly contaminated lakes. No record is given of this genus by Kofoid 

 from the Illinois Eiver. 



Microcystis Kiitz. {Polycystis Kiitz. Clathrocystis Henfrey.) 



Microcystis is represented in Lough Neagh by the species 



M. firma (Breb. et Lemm.). 

 M. aeruginosa Kiitz. 

 M. holsatica Lemm. 



M. firma and M. holsatica are recorded for the first time for Lough Neagh. 

 M. prasina (Wittr.) Lemm., M. st'ignalis Lemm., and M. roseopersicina (Kiitz), 

 West, are recorded by Messrs. West in addition to the above. We have for 

 purposes of this report added the various species together. 



Microcystis is never common in Lough Neagh. It reaches a maximum in 

 February of 41,600 in the bottom-to-surface catch, and diminishes rapidly. 

 It is very rare from September to February. 



Wesenberg Lund records M. aeruginosa and AI. flos-aquae in all the 

 Danish lakes examined except Esromso, in which the former alone occurs. It 

 reaches its maximum in July, which may be very high. It is absent from 

 Ennerdale Water, Wastwater, Loch Earn, and Loch Lubnaig. 



M. e/abens and M.fios-aquae both occur rarely in Loch Lomond in October 

 and November and in August respectively. M. flos-aquae occurs in very 

 small quantities in June in Loch Katrine. 



Never in Lough Neagh, so far as we know, does Microcystis form " water - 

 bloom." This is not the case on the Continent, where it often is the charac- 

 teristic blue-green alga occurring in water-bloom. It has been observed on 



