PERIODICITY OF THE PHYTOPLANKTON OF SOME BRITISH LAKES. 409 
level. The lake-basin consists of outcrops of metamorphic and Devonian 
rocks. The collections were made to the north-west of Luss at monthly 
intervals from September 1908 to August 1909. 
Sept. 2nd, 1908. Temp. of water 59° F. (—15? C.). A mixed plankton 
consisting of Chlorophyeez and DBacillarie:e, with a considerable quantity of 
Celosphorium Kützingianum. Among the Chlorophyce certain species of 
Staurastrum, such as St. paradoxum var. cingulum, St. lunatum var. planetoni- 
cum, and others, stood out conspicuously, and Tetraspora lacustris and Ankis- 
frodesmus faleatus are quite соттоп. The only common Diatoms are 
Tabellaria fenestrata and Т. floceulosa. Rotifers abundant, but few Copepods- 
Oct. 2nd, 1908. Temp. of water 60° Е. (=15:5° С.). Very similar to the 
collections of the preceding month, but with less Ceratium Hirundinella, 
Celospheriun Kützingianum in great quantity. 
Nor. 2nd, 1908. Temp. of water 54° Е. (—12:2? €). Diminution in 
Chlorophyceee, more especially in number of Desmids. —Coelospharium still 
very abundant, but the colonies beginning to dissociate. Asterionella and 
Tabellaria fairly common. Copepods numerous. 
Dec. 1st, 1908. Temp. of water 49° Е. (=9-4° C.). Chlorophyceæ much 
reduced, although varieties of Staurastrum paradowum are still common. 
There is а great influx of detritus and a rapid diminution of Calospherium. 
The amount of Melosira granulata much increased. Copepods and Bosmina 
fairly common. 
Jan. 9th, 1909. Temp. of water 44? F. (=6°6° C.). АП the phyto- 
plankton greatly reduced, except the varieties of Staurastrum paradoxum and 
Melosira granulata. Few Rotifers, Nauplii, and Bosmina. 
eb, Ath, 1909. Temp. of water 43? F. (=61° C.). The plankton 
contains much detritus. Desmids scarcer than in January, but varieties of 
Staurastrum paradoxum not rare. Melosira granulata and Surirella robusta 
var. splendida both increasing in quantity. Few Rotifers and many Nauplii. 
March 2nd, 1909. Temp. 40° F. (=4:4° C.). Less detritus and more 
phytoplankton in the collections. Cælosphærium Kützingianum increasing 
in quantity. -Isterionella formosa common and Melosira granulata about as 
abundant as in February. Desmids present in increased numbers and 
showing signs of active division. Rotifers few, but plenty of Naupiii and 
Entomostraca, especially large specimens of Bosmina. 
April 3rd, 1909. Temp. of water 41° F. (—5? C). Very great increase 
in Diatoms, more especially Melosira granulata and Asterionella. The genera 
Eunotia, Navicula, Surirella, and Cyclotella well represented. — Desmids 
frequent, but obscured by abundance of Diatoms.  Cwlosphwrium Kütz- 
ingianum common. 
May 3rd, 1909. Temp. of water 45? Е. (— 72? C.). Diatoms entirely 
dominant, more particularly Melosira granulata. Asterionella not quite so 
