Fischerella sp.

Source of the photo: 
http://silicasecchidisk.conncoll.edu/Pics/Other%20Algae/Blue_Green%20jpegs/Fischerella_Key55.jpg
Author of the description: 
k
Fischerella sp.

The microscopical view of the species Fischerella. The branches tend to from the multiseriate portions of the main filaments. Note the shape difference between the narrow, elongated cells of the branches and the rounded cells of the main filament.