196 BRITISH DESMIDIE^. 



12. Cells not fasciculated Closterium. 



Cells fasciculated Ankistrodesmus. 



13. Frond an elongated jointed filament 14 



Frond of few cells not forming a filament 18 



14. Filament plane or triangular, with junction-glands or fora- 



mina between the joints 15 



Filament never plane ; neither glands nor foramina between 



the joints 16 



15. Joints with junction-glands; their margins incised or si- 



nuated Sphcerozosma. 



Joints with foramina between them; their margins bicre- 



nate or entire Aptogonum. 



16. Filament triangular or quadrangular Desmidium. 



Filament cylindrical or subcylindrical 17 



1 7. Joints surrounded by a groove Hyalotheca. 



Joints with two opposite bicrenate projections Bidymoprium. 



18. Cells arranged in the form of a flattened star Pediastrum. 



Cells placed side by side in one or two rows Scenedesmus. 



ANALYSIS OF THE SPECIES. 



1. Hyalotheca. 



Fragile ; joints bicrenate dissiliens. 



Scarcely fragile ; joints with a minute bifid projection mucosa. 



2. DiDYMOPRIVM. 



Joints broader than long ; with angular teeth Grevillii. 



Joints longer than broad ; with rounded crenatures Borreri. 



3. Desmidium. 



Filament triangular Swai'tzii. 



Filament quadrangular quadrangulatum. 



4. Aptogonum. 



Desmidium. 



5. Sph^rozosma. 



Constriction of joints a linear notch on each margin .... vertehratum. 

 Constriction a broad sinus on each margin excavatum. 



