132 EDITH M. PRATT, B.SC. 



Diaptomus gracilis, Sars. 



Diaptomus gracilis, Brady, Rev. Brit. Freshw. Cyc. and Cal. p. 29, pi. xi. 

 figs. 7-9, pi. xii. figs. 1-8. 



This species is universally distributed and abundant throughout 

 Britain in large sheets of water where there is little vegetation. 



(On making a revision of the material I feel doubtful if Diaptomus 

 castor occurred, and I have consequently struck it out of the list. 

 Nov. 20, 1899.) 



ROTIFERA. 



Asplanchna priodonta, Gosse. 



Asplanchna priodonta, Gosse, Ann. & Mag. Nat. Hist. ser. 2, vol. vi. 1850, 

 p. 18, pis. i. & ii. ; Hudson and Gosse, Rotifera, p. 123, pi. xii. fig. 2. 



Gosse found this species not uncommon in the Serpentine, Kensington 

 Gardens, and in ponds and ditches near Birmingham. It was very 

 sparingly but generally distributed in April, but in June occurred in 

 vast quantities in all the tow-nettings taken at the surface and 

 moderate depths. 



In the Map accompanying this paper the areas of depth are signified 

 by dotted lines. 



The weather was calm and fine when the tow-nettings were made in 

 June, but there had been heavy rains a few days before. 



The tow-nettings were confined to the middle and northern portions 

 of the lake. 



In the 10-fathom area six tow-nettings were made, and were 

 characterised by the presence of Polyphemus in greater numbers than 

 elsewhere, and the almost complete absence of Leptodora and Bytho- 

 trephes (a few immature forms were taken). 



In the 25-fathom area four tow-nettings were taken from 6 to 8 feet, 

 in which Leptodora and Byihotreplies were fairly common: 



In the 50-fathom area five tow-nettings were taken from 6 to 10 feet, 

 and in these gatherings Leptodora and Bythotrephes were very 

 abundant. (It is worthy of note that Leptodora and Bythotrephes very 

 often occur together in great abundance.) 



The remaining forms were distributed more or less universally over 

 the portion of the lake examined. 



