408 
BULLETIN OF THE BUREAU OF FISHERIES. 
(stations 81 to 88), and that Synchseta stylata W., absent in the lower part, was very- 
common at all stations above Point au Sable. The eggs of this species occurred very 
often also in the upper part of the lake and were not found at all in the part below 
Lake City. 
Special attention was given to the distribution of Leptodora kindtii. This 
organism was especially numerous in the upper part of the lake and in mid lake 
opposite Lake City. The distribution of Leptodora in the lake is shown on Figure 
19. The maximum abundance, 710 per cubic meter, was found at station 81, close 
to the shore. Many young Leptodora have been found in the upper part of the 
lake, whereas in the lower part only adults occurred. 
The behavior of Leptodora in lakes has attracted the attention of many investi- 
gators. It is generally known that at twilight this organism appears near the 
surface and during the day keeps in the lower strata. In Lake Pepin, at the sta- 
tions where Leptodora was most abundant (stations 81 and 86), its maximum 
during the daytime was found at the depth of 4 to 7 meters, but several specimens 
of it occurred also in the top water, especially in the shallow parts of the lake and 
near the shores. The writer has found in previous investigations in Lake Kossino 
(Russia) that the diurnal migrations of Leptodora are rather complicated. At 
nightfall the Leptodora in that lake move up to the surface water and toward the 
shores; at sunrise they return, hut some remain near the shore in the top water. 
There was no opportunity to study the dirunal movement of Leptodora in Lake 
Pepin because all observations were made between 8 a. m. and 5 p. m., but it was 
often noted that near the shores these forms occurred at the surface layer, while in 
mid lake the maximum occurrence was in deeper strata. 
The plankton collected amid the aquatic vegetation differs from that of the 
pelagic region mainly by a greater variety of diatom flora. The principal plankton 
forms are, however, the same as in other parts of the lake. Water plants grow in 
profusion in the lower shallow part of the lake close to the shores, beginning from 
Pepin village down to the delta of the Chippewa River. The bottom of the lake 
is covered here with Potomogeton crispus, P. americanus, Vallisneria spiralis, and 
Ruppia occidentalis, each of them forming separate associations. 
The most abundant diatom flora has been found among the Potamogeton 
associations. The following is the list of diatoms collected here and identified by 
Dr. Albert Mann : 
Cocconeis distans Greg O 
placentula E © 
Cyclotella menenghiniana Breb © 
Cymatopleura elliptica W. S O 
Cymbella, caespitosa K © 
cistula (Hemp.) Kirch Q 
Epithemia gibba (E) K © 
sorex K 3 
Gomphonema affine K © 
lanceolatum E O 
Melosira crenulata K 3 
Among the other water plants the diatom flora was the same as the foregoing 
except for one new form, Navicula radiosa K., which was rather abundant. 
Navicula amphigomphus E O 
Reinhardtii Grun O 
scutelloides W. S © 
Nitzschia palia (E) W. S O 
Pleurosigma Spenceri K © 
Stephanodiscus niagarse E Q 
Surirella minuta Br6b © 
Synedra delicatissima W. S © 
splendens K 0 
ulna v. capitata E © 
