188 Marsh — Limnetic Crustacea of Green Lake. 



Of plants, the only one besides diatoms, which occurred in 

 any abundance was the Anabaena already mentioned. In 1896 

 this appeared in the latter part of June, and continued well 

 through August. In other years, I have found it present only 

 during a very short time. I have notes also of a red alga that 

 was found in considerable abundance about the middle of 

 August. In one of the March collections there was also an un- 

 determined green alga. 



Rotifera were of course present in large numbers, but no at- 

 tempt was made to keep any record of them. Notholca longi- 

 spina was found throughout the year, sometimes in great abun- 

 dance. 



Ceratium occurred quite constantly in the collections from 

 June to the latter part of October, and in 1896, until the middle 

 of November. 



From May throngh the year, Diptera are occasionally found 

 in the collections. This is what one would expect, for the 

 larvae are found in the bottom fauna. 



METHOD OF COUNTING. 



The method used in counting was somewhat different from 

 that used by other authors, and a method that perhaps could 

 not be used so successfully in collections containing a large 

 amount of vegetable material. The alcohol in the bottles was 

 largely replaced by glycerine in order to have the material in a 

 medium that would not evaporate rapidly. I had prepared for 

 me a glass plate sixteen centimeters in diameter, ruled with con- 

 centric circles a centimeter apart. The circles were divided by 

 diameters^ into eight segments. The plate was mounted on 

 a tripod such as is used in leveling gelatine plates in bacterio- 

 logical work, and carefully leveled. The collection was then 

 poured as nearly as possible upon the exact center of the plate. 

 Ordinarily it would spread with great uniformity upon the 

 plate. The fractional part of the whole counted depended upon 

 the numbers of the species under consideration. Commonly I 

 counted only one-eighth of the Diaptomi. Of the species present 

 in smaller numbers, I would ordinarily count all on the plate. 

 In any case all parts of the plate were examined in order to de- 



