Dakin and Latarche — The Plankton of Lough Neagh. 53 



Wesenberg Lund records both these species for the Danish lakes, but 

 does not state in what quantities they occur or in what month they attain 

 their maximum. Apstein records a double maximum for Pediastrum in the 

 Baltic lakes, one in spring and a larger one in August. 



It is absent from Ennerdale Water, Wastwater, Loch Lomond, Loch 

 Katrine, Loch Earn, and Loch Lubnaig. West records the genus for the 

 Scottish lakes, Orkneys and Shetlands, west and south-west Ireland, Welsh 

 lakes, Lough Xeagh and Lough Beg ; but it is very uncommon. 



Pediastrum is widely distributed in the arctic lakes ; in the north 

 European lakes it occurs, but only in small quantities, although the number 

 of species may be large. Numerous species of Pediastrum have been recorded 

 from the Baltic lakes, but they occur only in small numbers. 



P. Boyyamim occurs in the plankton of the Illinois River in small 

 numbers during every month of the year. There are vernal and autumnal 

 maxima in May and September at similar temperatures. P. duplex is much 

 more abundant than P. Boryanum in the Illinois River; in fact, it is the 

 most abundant representative of the Chlorophyceae in these waters. The 

 seasonal variation is practically the same for both species. 



Staurastnim. 



Numerous species of this genus occur in the plankton of Lough Neagh, 

 but by far the most frequent species is ^. paradojntin var. loiigipes. For the 

 purpose of this work all the species have been counted together. 



It occurs throughout the year, but from the month of March until 

 early in July it is present only in very small quantities. In September it 

 reaches a maximum of 388,540 for all the catches. 



Wesenberg Lund states that S. gracile and S. paradoxum var. longipes 

 occur in the Danish lakes, the latter only rarely and the former in small 

 quantities. 8. gracile reaches its maximum in the summer months, viz., July 

 and August. Apstein records S. gracile from the Baltic lakes, where it attains 

 its maximum in August. It is at its minimum or absent altogether from 

 March to June. 



W. and G. S. West record several species of Staurastrum from Ennerdale 

 Water, ,5'. jacvliferum West forma hiradiata being the most common. It 

 reaches its maximum in August, and is rare in January and March. In 

 Wastwater, S. jaculiferum West (f. triradiata) is very common from June to 

 November, and rare from February to April. Staurastrum is present in small 

 quantities in Loch Lomond, while in Lough Katrine it occurs in much larger 

 quantities. Here West finds that S. paradoxum- has its maximum from May 

 to July, while S. paradoxum var. longipes has its maximum from August to 



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