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, G-reen 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 G-reat 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 



