D. pulicaria. 
469 
Period IV.— Aug. 1-4. 
Depths. 
Average. 
Day. 
Night. 
Meters. 
No. 
Per cent. 
No. 
Per cent. 
No. 
Per cent. 
0-3. 
113 
43.5 
124 
45.7 
98 
39.7 
3—6. 
69 
26.5 
73 
27 
66 
26.7 
23.5 
6-9.. ... 
61 
23.5 
65 
24 
58 
9—12. 
16 
6.15 
8 
3 
24 
9.7 
12—15. 
0 
0 
0 
0 
0 
0 
5—18. 
1 | 
j .39 
1 
.3 
1 
.4 
Total. 
260 
271 
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 0 (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 dale 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 
