D. pulicaria. 



469 



Period IV.— Aug. 1-4. 



Depths. 



Average. 



Day. 



Night. 



Meters. 



No. 



Per cent. 



No. 



Per cent. 



No. Per cent. 



1 



0-3 



113 



43.5 



124 



45.7 1 



i 



98 



39.7 



3—6 



69 



26.5 



73 



27 



66 



26.7 



6-9 



61 



23.5 



65 



24 



58 



23.5 



9-12 



16 



6.15 



8 



3 



24 



9.7 



12—15 



























5—18 



1 



.39 



1 



.3 



1 



.4 



Total 



*60 





271 



1 



247 









Daphnia pulex, var. pulicaria Forbes. 



This species of Daphnia is very closely related to the Euro- 

 pean form D. schoedleri Sars, and is possibly identical with it.. 

 In general appearance it closely agrees with D. pulex, as also in. 

 the armature of the post-abdomen, and in the teeth of the cau- 

 dal claw. The chief difference lies in the transparency of the- 

 animals. Specimens belonging apparently to this species are 

 found near Madison in temporary pools, and in such situations,, 

 while not showing the yellow tint characteristic of D. pulex 

 they become opaque, having a grayish white color. In the open- 

 lake, however, they are nearly as transparent as D. hyalina. 



This species was the smallest in number of the forms which 

 regularly appeared in our dredging. The average number for. 

 the whole period was 103, with a maximum of 279 (J. 19, 9 a. m.) 

 and a minimum of 1 (A. 2, 3 a. m.) and (3 obs., Aug. 2 and 

 3). The number varied greatly in the different periods, the 

 agerage in Period I being 101; in Period II, 135; in Period III, 

 125, and in Period IV, 18. These numbers indicate the disap- 

 pearance of the species early in August, and this conclusion is 

 confirmed by the fact that in later observations only single in- 

 dividuals have appeared. The latest date at which a single speci- 

 men occurred was December 1, but no other individuals had been 

 found in the preceding two months or more. D. pulicaria aver- 

 aged about 1.5 per cent, of the total number of Crustacea caught. 



