390 _ BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Chlorosphera lacustris Snow, new species (fig. XIV). 
Individual cells 9 to 10.5 /¢ in diameter, spherical or ellipsoidal, usually in complexes of 2, 4,8, 
or more, formed by vegetative division, including membrane and contents; chloroplast concave; 
pyrenoid present; membrane thin, of cellulose. Zoospores 6.5 to 9 long, and 2.6 to 4 4 broad, 
oval, larger at the posterior end; two cilia present, a pyrenoid, a pigment spot, and 2 contractile 
vacuoles; 4 to 8 zoospores formed in a cell, liberated by the softening of the membrane at one point. 
Locality, the plankton of Lake Erie. 
Chlorospheera parvula Snow, new species (fig. XV). 
Cells usually in complexes of 4 or 8, more or less separated from each other by the partial dis- 
solution of the membrane. Diameter of cells 7.8 to 9 4; chromatophore concave, with a circular 
opening near the newest portion of the membrane. Pyrenoid present; membrane of cellulose; 
zoospores oval or round, 5 to 6 4c in diameter, 4 formed in each cell, liberated by the softening of 
the entire membrane. Locality, the plankton of Lake Erie. 
Celospherium roseum Snow, new species (fig. XVII). 
Colony 35 to 52 in diameter; cells spherical, pinkish or brown, 3.25 to 4 in diameter, arranged 
more or less closely over the surface of the gelatinous center; the gelatinous center not homogene- 
ous, but containing a system of dichotomously branched gelatinous stalks, on the ends of which are 
borne the cells: in the spaces between the gelatinous branches and surrounding the whole is a less 
dense gelatinous substance. Common in the plankton of Lake Erie. 
Chroococcus purpureus Snow. new species (fig. XVIII). 
Cells spherical, or just before division elongated, usually arranged 2 by 2 in colonies of 4 or 8, 
separated from each other and held in place by an enveloping gelatinous substance; color a gray- 
ish purple, changing to brown under unfavorable conditions. Cells when dying assume a dark 
blue-green, and the gelatinous envelope is sharply outlined. Common in the plankton of Lake Erie. 
LIST OF PLANTS DETERMINED IN LAKE ERIE. 
In the following list no account is taken of the number of individuals found, or 
of the relative number found during the different years, as no accurate quantitative 
work was done by the writer; but, had such a study been made, it is probable that 
interesting results would have been obtained. For instance, during the summer of 
1898 Kirchneriella obesa (West) Schmidle was one of the most common of all the 
Chlorophycee found in the plankton, while in 1899 it was found but a very few 
times, and in 1900 only occasionally. During its absence in 1899 its place seemed 
to be taken by Oocystis borgei, which the preceding year had not been noted at all, 
and the next season was found only in very small quantities. An equal variation 
was noted in the occurrence of different forms from week to week during each year. 
Certain forms, such as Anabena flos-aque, appeared in quantities for a few days 
and then disappeared almost altogether. The number of diatoms also varied very 
largely at different times. An explanation of such variations would undoubtedly 
involve a more accurate knowledge than we now have of the composition of the 
water, as well perhaps as of other elements in the environment. 
In the collections of the plankton numerous fragments of filamentous algze— 
Spirogyra, Zygnema, Mesocarpus, didogonium, and Bolbochete—were often found, 
but as no stages of reproduction were present they could not be determined, and so, 
except in a few cases, no mention is made of them. 
The species that are not starred were taken from the plankton. Those marked 
with one star were found in washings of stones and of plants growing in the lake. 
Those marked with two stars were found in Lemna Pond, South Bass Island, and 
those marked with three stars were found in a stagnant pond on Middle Bass Island. 
