WISCONSIN PHYTOPLANKTON 173 



var. COHAERENS Bohlin. PL 48, Figs. 3-4. 



Bih. t. Kgl. Sv. Vet.-Ak. Handl. 23, Afd. 3, No. 7: 31, pi. 2, fig. 1. 1897. 



Pediastrum duplex var. reticulatum forma cohaerens (Bohlin) Brunnthaler, 

 in Pascher, D. Siisswasserfl. Deutschl., osterr. u. d. Schw. 5 2 : 95, fig. 57e. 1915. 



Coenobia circular to oval, of 16-32-64 cells, with median-sized inter- 

 cellular spaces. Wall of cells covered with short, linear, concentrically 

 arranged granules. (Facultative Planktont). 



Cells 12-22 p broad; 13-24 f*. long. 



Pine Tree (r). 



PEDIASTRUM BIRADIATUM Meyen. PI. 48, Figs. 5-8. 



Nova Acta Phys.-Med. Ac. Caes.-Leop. Nat. Cur. 14 2 : 773, pi. 43, figs. 21-22. 1829. 

 Pediastrum rotula (Ehrenberg) A. Braun emend. Alg. unicell. 101, pi. 6, 

 figs. 2-3, 5-7, 10, 12-14. 1855. 



Coenobia of 4-8-16-32-64 cells, with medium sized openings between 

 cells. Marginal cells in contact with one another at base only, with 

 two long projections that are dilate and incised at the apex. Interior 

 cells as those of the margin but apices of projections neither dilate nor 

 incised, in contact with other cells at base and ends of projections only. 

 Cell wall smooth. (Facultative Planktont). 



Cells 10-22 p, broad, 15-30 p. long. Diam. 32-celled coenobia 80-150 /A. 



Balsam (rrr), Bear (3) (rr), Big McKenzie (rr), Lac du Flambeau (rr), 

 Mud (2) (rr), Nancy (rrr), Pokegama (1) (rrr), Wolf (rrr). 



This species resembles P. duplex var. reticulatum in the perforation 

 of the disc but differs in the deep incision of the marginal cell projec- 

 tions. Perfect colonies are seldom seen since apices of projections of 

 certain interior cells are free and have the same dilation and incision 

 that is found in the marginal cells. The number of cells in the colony 

 is generally stated as 8-16-32 but the coenobia in the plankton of Wis- 

 consin lakes are 32- or 64-celled except in very rare cases. 



PEDIASTRUM TETRAS (Ehrenberg) Ralfs. PI. 48, Figs. 9-12. 

 Ann. & Mag. of Nat. Hist. 14: 469, pi. 12, fig. 4. 1844. 



Coenobia rectangular, oval or circular; without perforations; of 

 4_8-16-32 (generally 4-8) cells. Outer face of marginal cells with a 

 single deep linear to cuneate incision, the halves of the outer face 

 slightly to deeply emarginate. Interior cells with a single deep linear 

 incision and 4-6 straight sides. Cell wall smooth. (Tychoplanktont). 



Diam. cells 8-15 /*. 



Blake (rrr), Browns (rrr), Chain (rrr), Chetek (rr), Cochrane (rrr), Hill- 

 man (rrr), Horse (rrr), Horseshoe (2) (rrr), Kimball (rrr), Lindy (rrr), 



