HOW TO KNOW THE FRESH-WATER ALGAE 

 192b Interlocking polar processes not slender and horn-like 193 



193a Interlocking processes in the form of forked lobes which bear 

 recurved hooks. See Fig. 110 MICRASTER1AS 



193b Interlocking processes simple, short and tuberculate. Fig. 134. 

 SPHAEROZOSMA 





Fig. 134. Sphaerozosma excavata 

 Ralfs. 



This is a filamentous desmid in 

 which the cells are adjoined by 

 the interlocking of the polar pro- 

 cesses themselves. None of the 

 Figure 134 species bear spines but they usu- 



ally have minute granules at the 

 angles of the semicell, or forming transverse bands across the semi- 

 cell. This genus usually occurs in acid lakes, intemingled with other 

 desmids. 



194a (191) Semicells transversely elliptic or oval, the median incision 

 of the cell deep. Fig. 135 SPONDYLOS1UM 





Fig. 135. Spondylosium sp. 



Although this genus can have 

 Figure 135 cells that are triangular in end 



view, most species have cells, that 

 are compressed and are somewhat like Cosmarium (Fig. 113) in a 

 filament. One species which is rather rare is S. pulchrum (Bail.) 

 Archer. It has semicells which are much extended laterally so that 

 the cell is much wider than long. The apices of the cells in this 

 are furnished with a protrusion which adjoins that of the adjacent 

 cells in the filament. The walls are smooth and undecorated. 



194b Semicells not transversely elliptic, median incision not deep, 

 sometimes only a slight concavity of the lateral wall 195 



195a Cells cylindrical, subcylindrical, or barrel-shaped 196 



195b Cells quadrate or angular, usually with the margins conspicuous- 

 ly lobed. (See Fig. 138b, Desmidium Bailey i, however) 197 



89 



