426 Wisconsin Academy of Sciences, Arts, and Letters. 
b. Cells with polar bulbs or thickenings. 
X. Cells acicular with small polar bulbs, 
apices of cells pointing away from center 
of coenobe. 
6. S. antennatus de Breb. 
XX. Cells blunts spindle shaped, with polar 
nodules. Wall of cell convex on side away 
from center of coenobe, concave towards 
center. 
7. S. incrassatulus Bohl. 
B. Cells ovoid. 
a. Outline of cell perfect oval. 
X. Cells in a linear or alternating series, never 
in a double series. 
8. S . bijug a (Turp.) Lag. 
XX. Cells arranged in two series. 
*. Cells alternately arranged, large inter¬ 
stices between cells, coenobe curved. 
9. S. curvatus Bohl. 
**. Cells in two series, interstices between 
cells small, coenobe curved or flat. 
10. S. arcuatus Lemm. 
b. Cells with capitate ends. 
11. S. producto-cap itatus, Schmula. 
2. Cell membrane with teeth at poles, without spines, 
ridges or external ornamentation in the middle of 
the cell. 
A. 2-3 teeth at each pole. 
12. S. denticulatus Lag. 
B. Several teeth at poles of cells. 
13. S. acueolatusHeinsch. 
3. Cell membrane with longitudinal ridges, with or 
without spines or teeth. 
A. Cells with longitudinal ridges only. 
a. Middle cells with a ridge on each side, and 
cells with four ridges. 
14. S. acutiformis. Schroder. 
b. Cells with four to six longitudinal ridges on all 
cells. 
15. S. costatus Schmidle. 
B. Cells with longitudinal ridges and teeth on poles. 
16. S. brasiliensis. Bohlin. 
