Marsh—Limnetic Crustacea of Green Lake. 181 
springs on the south shore, and it is popularly supposed that 
most of the water is derived from this source. 
The water of the lake is clear, of a beautiful green color, and 
reaches a maximum depth of two hundred and seventeen feet. 
The bottom in the deep water consists of a fine, blue clay, con¬ 
taining a large amount of organic matter, in which are 
found worms, none of which have been determined. 
In the general character of its fauna, Green Lake resembles, in 
a striking manner, the Great Lakes. In its abysmal fauna, we find 
Pontoporeia Hoyi and My sis relicta ,— species which have not 
been found in America outside of the Great Lakes. In the 
intermediate depths is Limnocalanus macrurus ,—a species sel¬ 
dom found except in the larger bodies of water, and in the upper 
layers are found the same species as in the Great Lakes with 
two exceptions,— C. pulchellus and D. Ashlandi. There is never 
any striking amount of vegetable matter in Green Lake except 
in the months of July and August, when ordinarily an Anabaena, 
which I think is either flosaquae or circinalis is found all over the 
lake, and forms little green ridges as it is washed up on the 
shore by the waves. But even this is not present in sufficient 
amount to form a scum, and never fouls the collecting net to 
any extent, as does the “scum” of shallower lakes. 
Apstein divides lakes into two groups, which he styles Chro- 
occaceae lakes and Dinobryon lakes. According to the general 
characteristics which he gives to these two groups, Green Lake 
should be a Dinobryon lake, and yet I have never found Dinobryon 
in it. 
It seems to me that our lakes in this part of North America 
can naturally be divided into the two classes of “deep” and 
“shallow” lakes, the faunae of the two classes being very distinct 
in their general character. The “shallow” lakes have, in the 
summer season, a large amount of the chlorophyll bearing algae; 
there is but little distinction between the littoral and limnetic 
species of Cyclops ; Limocalanus macrurus is seldom present; and 
the abundant species of Diaptomus is oregonensis. Epischura 
lacustris may be present in shallow lakes, but is not always 
found. 
In the deep water fauna of the “deep” lakes the common 
