22 HENRIK PRINTZ [1920 
contents of some few cells have formed ovoid zoospores by simul- 
taneous divisions. 
This alga thus having zoospores, a way of reproduction that is 
not known to take place in the true genus Protococeus — as I consi- 
der the statements of this as very problematic — and as the alga in 
question further is lacking the divisions so characteristic of. Proto- 
coccus, it differs so widely and in 'so essential characters, that it 
appears to belong to a totallv different genus. I therefore provi- 
sionally class it as Pleurastrum lobatum, and give the following 
diagnosis: 
Celiulis inflatis, rotundatis, vulgo 7—12 u, raro usque ad 15 u 
diametro, plerumque colonias 2—4 cellularum, vel majores in uno 
plano sitarum formantibus. Membrana hyalina, tenerrima et levi, 
raro tenuiter crenulata. Ghromatophoro 1, raro 2, parietali, lamnini- 
formi, margine vulgo irregulariter lobato, latere uno partem 
achroam vulgo relinquente. Pyrenoidibus nullis. Nucleo pro ratione 
magno, cenitraliter sito. Propagatio cellulis in plana duo inter 
se perpendicularia successive divisis. Zoosporis ovatis divisionibus 
simultaneis contentus cellularum ortis, membrana materna tenui 
dirupta liberis. Zoosporis 2—5 u longis. 
It is extraordinary that such an exceedingly frequent species, 
apparently occurring nearly all over the world, has not earlier been 
more completely known. Ås a rule it will be met with only as 
2—3- or 4-celled colonies, in which the morphological conformity to 
the genus Protococcus is absolute. That the divisions take place in 
Iwo, directions only, is, accordinglv, not possible to observe in such 
cases, as the cells after the divisions disintegrate to quickly. In 
some samples, however, I have not unfrequently met with this 
species as larger colonies, an appearance possibly owing tio external 
conditions. Åt times, also solitary spherical or ovoid cells are to be 
found. Fig. 164, pl. IV shows a solitary cell in zoospore-formation. 
Fig. 165—168 represent progressive stages of cell-divisions. 
The membranes in this alga are very thin, hvaline and smooth. 
Just as in other subaérial algae, I have also in this species at times 
observed cells with finely crenulate membranes, however. The size 
of the cells is usually 7—12 pu, sometimes up to 15 u In diameter, 
and down to 5—7 u im diameter. The divisions are rather irregular, 
and colonies consisting of three cells are not unfrequently to be 
seen. The chromatophore is cup-shaped, with partly incised edges. 
There is no pyrenoid. The zoospore-formation has not been common 
in any of the samples, and is certainly rare in free nature. It is 
possible, or even probable, that this only is limited to certain 
seasons, or is dependant on particular external conditions. It 
appears from the pictures that the formations of zoospores may 
take place in one or several cells of the same colony at the same 
time. The regular way of reproduction is, undoubtedly, by cell- 
