125 
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 charon (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. Miull.*—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 1s great and 
decaying organic matter abundant. 
Lionotus spp.—Average number, 94. With Amplileptus in the 
winter plankton there occur a number of other, smaller, gymnostome 
ciliates which in best-preserved specimens resemble Lionotus. A tew 
occurring in March and April, 1898, were found to be L. jfasciola 
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 Lzonotus coincides very closely 
