PLANKTON ALGiE OF LAKE ERIE. 
381 
This species certainly resembles closely the Oocystis laeustris described by Chodat ’97, but 
after cultivating the two forms, both of which occur in Lake Erie, and obtaining an abundance of 
pure material of both, each was found to show certain characteristic differences which separate 
them into different species. The most striking of these was the protruding point at the ends of the 
cell of Oocystis laeustris, while in the other species, if any thickening was noticeable at the poles, 
it did not project in the form of a wart, but was a gradual thickening of the membrane. Another 
difference, which was constant, was the longer and more slender shape of Oocystis laeustris. 
From the figure given by Borge, 1900, of a form occurring in Sweden, it would seem that the 
species in question must be the same, though the dimensions are slightly smaller than those given 
by Borge. In recognition of Borge having first figured the species it has been called Oocystis borgei. 
Chodatella citriformis Snow, new species. 
This new species is distinguished from other species of this genus by the shape of the cell, there 
being a short, obLise elongation at either end, and at the base of these are arranged the whorls of 
spines which characterize the genus (fig. vm, 1, 2, 3). 
The length of the cells varies from 8 to 10 ju. The spines are very delicate, often 33 to 36 y 
long and but 0.5 /< broad at the base. In different individuals six, seven, eight, and nine spines 
were found. It was not thought by the author, however, that these represented different species, 
although some authors seem to distinguish different species by the number of spines. Unfor- 
tunately, large cultures of this species were not obtained; and although cells were observed through 
several generations in hanging drop cultures, it could not be determined whether or not the num- 
ber of spines was constant in the descendants of a single individual, for as soon as an individual 
was confined in a hanging drop, the spines became gradually indistinct, finally disappearing, and 
the daughter individuals possessed either no spines or very rudimentary ones. Apparently the 
spines were of a gelatinous nature. In the test for cellulose with iodine and sulphuric acid they 
quickly disappeared when the acid was added. The reaction for cellulose was obtained in the 
membrane. 
The chlorophyl is contained in a single parietal chloroplast, leaving the opposite side colorless. 
A pyrenoid lies embedded in the chloroplast. 
The reproduction occurs by the cell contents becoming divided into two, four, and sometimes 
eight parts. Each becomes invested with a membrane , and forms a daughter individual (fig. vm, 3) . 
Though the actual process of liberation of the cells was not witnessed by the author, due to insuf- 
ficient material, it was inferred that they were set free by the rupturing of the membrane, as 
membranes were found which were undoubtedly the empty mother membranes of this species. 
Chodatella citriformis was found in surface tow and at a depth of about 10 meters, near North 
Bass Island, in Lake Erie. 
Pleurococcus regularis Artari. 
One of the most conspicuous and common of all the plankton algae is a form determined by 
the writer as Pleurococcus regularis Artari (fig. ix, 1). It consists of cell complexes composed 
usually of 4, 8, 16, or 32 clusters of cells, more or less separated from each other and embedded in 
a transparent, gelatinous substance («). Each cluster in turn is composed of 4, 8, 16, or 32 cells, 
which may be in contact with each other or may be separated from each other and held in place 
by the same gelatinous material. Without doubt it is these complexes which Senn ’99 regards as 
stages in the development of Coelastrum microporum Naeg. , and Chodat as stages of Coelastrum 
spheerium Naeg. The striking resemblances of these complexes to Coelastrum was noted by the 
writer when the alga was first seen in the plankton. The view held by Chodat as to the identity 
of the two forms was then accepted and the difference in appearance was regarded simply as dif- 
ferent phases of the same form, due to different conditions. It was noted, however, that side by 
side in the large plankton cultures, as well as in the fresh collections, both forms were found. The 
one corresponding to Coelastrum consisted of single, isolated ccenobia composed of many closely 
arranged cells with very little surrounding gelatinous substance. The other form consisted of 
many clusters, widely separated from each other and embedded in a common gelatinous matrix. 
The individual cells also, as well as the coenobia, were more or less separated from each other 
according to age. With a view to determining definitely whether these were the same species in 
different stages or distinct forms, each was isolated and placed in culture under the same condi- 
