1168 Wisconsin Academy of Sciences, Arts and Letters. 
niesl. For the concurrent forms there is only the single possi¬ 
bility shown in Text Figure 5 A. The nonconcurrent nonco- 
planar forms may have their axes either parallel (Text Figure 
5 B) or nonparallel (Text Figure 6.) The only known par¬ 
allel nonconcurrent noncoplanar arrangemjent of the cells, is that 
r\ 
ebb 
A B 
Figure 5. Possible combinations of the four cells of a coenobe in a colinear 
noncoplanar or a parallel nonconcurrent noncoplanar series. Shaded dia¬ 
grams represent those arrangements which are known to exist in nature. 
found in Tetradesmus wiscominensis Smith. There are no algae 
which can be regularly classified as nonparallel noneoncurrent 
noncoplanar forms, although, as will be later pointed out, 
Scenedesmns acutus Meyen may at times have the cellular ar¬ 
rangement shown in the shaded portion of Text Figure 6. 
Arranging the possible combinations of the four-celled coeno- 
bie algae in a table, we have the classification given below. All 
of these possibilities are illustrated in Text Figures 1-6, the 
shaded diagrams representing the forms known to occur in na¬ 
ture. 
I Cells Isoaxial. 
1— Linear colonies. 
2— Plane colonies : Tetraccocus botryoides West. 
3— Pyramidal colonies: Coelastrum microporum Naeg. 
II Cells Ileteraxial. 
1—Coplanar series. 
A—Concurrent forms. 
a—Colinear colonies. 
b—bJonparallel colonies: Pediastrum Bory- 
anum (Turp.) Meng., Crucigenia 
(Kirch.) W. & G. S. West, Tetras- 
trum Staurogeniaforme (Schrod.) 
Chodat. 
