SYNOPSIS OF THE GENERA. 



Fam. DESMIDIE^. 



Freshwater, figured, mucous and microscopic Algae, of a green 

 colour. Transverse division mostly complete, but in some genera 

 incomplete. Cells or joints of two symmetrical valves, the junction 

 always marked by the division of the endochrome, often also by a 

 constriction. Sporangia formed by the coupling of the cells and 

 union of their contents. 



* Plant an elongated jointed filament. Sporangia orbicular, smooth. 



1. Hyalotheca. Filament cylindrical. 



2. Didymoprium. Filament cylindrical or subcylindrical ; joints witli 



two opposite bidentate projections. 



3. Desmidinm. Filament triangular or quadrangular ; joints connected 



by a thickened border. 



4. Aptogonum. Filament triangular or plane, with foramina between 



the joints. 



5. Sphserozosma. Filament plane, margins incised or sinuated ; joints 



with junction glands. 



** Frond simple from complete transverse division, distinctly con- 

 stricted at the junction of the segments, which are seldom 

 longer than broad. Sporangia spinous or tuberculated, rarely 

 if ever smooth, 



6. Micrasterias. Lobes of the segments incised or bidentate. 



7. Euastrum. Segments sinuated, generally notched at the end, and 



with inflated protuberances. 



