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always found in Epistylis when they appear in Carchesium. This 

 degree of similarity in the seasonal cycle of the two genera is indica- 

 tive of their correlation with the same environmental factors, the 

 principal one of which is the increase in bacteria attending the colder 

 months. 



Euplotes char on (O. F. Mull.) Ehrbg. was taken but once in the 

 plankton August 23, 1898. 



Euplotes patella Ehrbg*. Average number, 2,888. It was found 

 in small numbers and at irregular intervals from April to December 

 throughout the full range of temperatures. It was most frequently 

 taken in the summer. 



Glaucoma scintillans Ehrbg.* Average number, 39,615. This 

 species was taken in the plankton from the middle of October till the 

 middle of April. It was present in larger numbers and more contin- 

 uously in December and February. It is thus a member of the 

 plankton during the time of bacterial increase. 



Halteria grandinella O. F. Mull.* Average number, 255,769. 

 The seasonal distribution of this species in the plankton does not 

 show the limitation to the winter months noted so frequently in other 

 ciliates. It was found in every month of the year but May, in largest 

 numbers in July and August, and most continuously in December and 

 January. The data are too few and irregular to determine any pre- 

 dominance as to season or temperature. 



Holophrya simplex Schew. was found in small numbers in the 

 filter collections of December, February, and March in the winter of 

 1896-97 at temperatures from 32 to 44. 



Leucophrydium putrinum Roux. Average number, 525. This 

 species was recorded July -September, 1898, during the low-water 

 period, at temperatures from 89 to 63. It was described by Roux 

 ('99) from stagnant water, but in our plankton no conditions of stag- 

 nation attend its presence, though sewage contamination is great and 

 decaying organic matter abundant. 



Lionotus spp. Average number, 94. With Amphileptus in the 

 winter plankton there occur a number of other, smaller, gymnostome 

 ciliates which in best-preserved specimens resemble Lionotus. A few 

 occurring in March and April, 1898, were found to be L. fasciola 

 Ehrbg. , and it is probable that most of the individuals belong to this 

 species, though exact identification is difficult with plankton mate- 

 rial. The seasonal distribution of Lionotus coincides very closely 



