WISCONSIN PHYTOPLANKTON 133 



KEY TO THE SPECIES. 



Cells arcuate, never sickle-shaped S. WESTH 



Cells arcuate to sickle-shaped. 



Diameter of cells not exceeding 5 n S. GRACELE 



Diameter of cells 5-8 p S. BIBBAIANUM 



SELENASTRUM GRACILE Reinsch. PI. 31, Fig. 5. 

 D. Algenfl. d. mitt. Th. v. Franken 65, pi. 4, figs. 3a-3i>. 1867. 



Cells lunate to sickle-shaped, quite narrow in proportion to their 

 length. Apices of cells acute. Chloroplast single, laminate, parietal, 

 on convex side of cell. Without a pyrenoid. (Facultative Planktont). 



Diam. cells 3-5 /*; length 15-30 p.. Distance between apices 8-20 p. 



Bear (3) (rr), Chain (rr), Hillman (rrr), Horse (rr), Monona (r), 

 Pokegama (1) (rr), Prairie (rr), Upper Turtle (rrr), Whitefish (rr). 



Differs from the next species in the more delicate cells. Possibly it 

 should be considered a variety of S. Bibmianum and not a distinct 

 tpecies. 



SELENASTRUM BIBRAIANUM Reinsch. PI. 31, Figs. 6-7. 

 D. Algenfl. d. mitt. Th. v. Franken 64, pi. 4, figs. 2*^-2*. 1867. 



Cells in spherical to ovoid colonies of 4-8-16 or more with their con- 

 vex sides facing the center of the colony. Cells crescent-shaped to 

 sickle-shaped, gradually tapering to a fairly sharp apex. Chloroplast 

 parietal, on convex side of and almost filling the cell ; pyrenoid single. 

 ( Facultative Planktont ) . 



Diam. cells 5-8 p. ; length 20-38 p.. Distance between apices 5-25 /*. 



Beaverdam (rr), Blake (rrr), Bone (rr), Deer (rrr), Little Bass (2) (rrr). 

 Loveless (rr), Mendota (rrr), Meta (r), Nancy (rr), Pewaukee (rr), Pine 

 Tree (rr), Poor Farm (rr), Rice (1) (rr), Spirit (rrr), Squirrel (rrr), Ten- 

 derfoot (rr), Travis (rr), White Ash (sss), Wolf (rr). 



All descriptions of S. Bibraianum state that there are but four or 

 eight cells in the colony but I have found that in Wisconsin lakes there 

 may be over a hundred cells in the colony, the number of cells usually 

 ceasing to be a multiple of two after there are more than sixteen cells 

 in the colony. 



Selenastnun Westii sp. nov. PI. 31, Figs. 8-10. 



Selenastrum acuminatum G. S. West non Lagerheim, Jour, of Bot. 50: 88, 

 figs. 5a-5s. 1912. 



Colonies of 2-4-8 cells irregularly arranged with their convex sides 

 in apposition. Frequently dissociating into the individual cells when 



