DaivIN and Latarche — The Plankton of Loiic/h Neagh. 55 



March, and is absent in June and January. It appears to have a double 

 maximum ; but aa it occurs in such small quantities, it is difficult to state this 

 definitely. It is not recorded from Wastwater, Loch Katrine, or Loch 

 Lubnaig. It is present in extremely small quantities in Loch Lomond in 

 Januajy and in Loch Earn in August. 



Wesenberg Lund records B. 'pvlchellum fr-om the Danish lakes. In Lake 

 Esromso it reached a great maximum in September. 



B. pulchelluin is typical of the North European lakes only. 



Eudorina. 



Eudoriiia chgans Ehrenb. occurs in the plankton of Lough Xeagh in very 

 small numbers from July to December. The numbers are at their highest 

 from August to October, reaching 18,500 in all the catches combined. It 

 disappears in January, and does not appear again until July. 



Messrs. West do not record Eudoiina from those lakes examined quanti- 

 tatively by them. Apstein records E. clegans from the Ploner See, where it 

 occurs from July to ISTovember, reaching its maximum in August. Wesenberg 

 Lund observed Eudorina in all the Danish lakes examined by him. Eudm-ina 

 ekgans has been recorded from east and west Greenland and from Nova 

 Zembla. It occurs also in the north European lakes and the Baltic lakes. It 

 is fairly common in the central Eiu'opean alpine lakes. 



This species is recorded from the Illinois Eiver by Kofoid, where it occurs 

 from February to October and in smaller numbers, and sporadically, during 

 the colder months. The maximum occurred in April. 



Tribonema. 



Tribonema homhi/cinum, forma depaAtperata Weille, occurs in Lough Xeagh 

 in fairly large quantities, although it is never so abundant as OsciUatoria or 

 Melosira. It is almost identical with Oedogoniiun, and has probably been 

 mistaken for the latter. Messrs. West make no mention of T. honihycinvm. 

 Our species has been kindly determined by Lemmerman. 



It is present in the plankton of Lough Xeagh through the year, reaching 

 its maximum ia March (950,000 ia the bottom-to-surface catch). During 

 April and May it diminished to 100,000 ; and in August it rose again to 

 420,000. It is at its minimum dm-iug November, December, and January. 



Messrs. West do not record 'Tribonema bomhycinum from any of the British 

 lakes examined by them, but Oedogonium sp. (sterile), with which it may have 

 been confused, occurs in aU these lakes very rarely. 



In Loch Lomond Oedogonium is less rare in March, August, and in 

 September, while in Loch Katrine it is fairly common in August, September, 



