Dakin and Latarche— T/^tf IHunkton of Lough Neagh. 59 



north Germany during the months of February, March, and April, when it 

 occurred in very small numbers. Murray records N. striata as a pond species, 

 rare at the margins of lakes in Scotland. N. striata is recorded by Kofoid in 

 the Illinois Eiver. It is a winter planktont, appearing in November, and 

 attaining its maximum in March and disappearing in April. 



Thus it wiU be seen that in Lough ISTeagh, Denmark, the Baltic lakes, and 

 America the species occurs in the same period of the year — a striking example 

 of the uniformity of fresh-water species with cofsmopolitan distribution. 



Mastigocerca. 



Mastigocerca cajmcinti Zach. and Wierz.— Appeared in the plankton of 

 liough Neagh in extremely large numbers in August and September. It was 

 not observed at any other time. 



Wesenberg Lund records it from the lakes of Denmark, where it occurs 

 from May to October -November. In Tureso it was observed on January 31st. 

 Apstein records it from Dobersdorfer See, where it appears in June, attains 

 its maximum in August, and disappears in November. In the Ploner See it 

 occurred in July, 1893. In 1892 it reached its maximum in the latter part of 

 September, and was absent in November. 



Murray does not record it from the Scottish lakes. 



It is absent from the arctic region, and occurs as a summer form in the 

 north European, Baltic, and the Swiss lakes. Amongst other Eotifers 

 occurring were : — 



Metopidia lepadella Ehrenbg. 



M. oscipternum Gosse. 



Synclineta pectinata Ehrenbg. (specimens fully contracted). 



COPEPODA. 



Cyclops strenuus Fischer. — Occurs in the plankton of Lough Neagh in large 

 numbers. It is present throughout the year. In July there is a maximum 

 of 3,425 in the combined catclies, after which there is a descent to 1,600 in 

 September. The number then rises rapidly until it reaches 4,722 in October, 

 after which the numbers remain high until February. 



Wesenberg Lund has obtained a similar seasonal variation for C. stremms 

 in the Danish lakes, although the first maximum there occurs in springs 

 Apstein does not record G. strenuus from the Baltic lakes ; but it is probably 

 present, and recorded in later works. Murray records it as general in the 

 Scottish lakes, where it occurs all the year round. C. strenuus occurs in the 

 plankton of the arctic regions, where it is one of the main forms of the large 



B.I.A. PKOC, VOL. XXX., SECT. B, [7] 



