118 WISCONSIN PHYTOPLANKTON 



Cells triangular, flattened, concavity of sides very marked. Angles 

 of cells ending in short spines. Several parietal, disciform chloroplasts 

 without pyrenoids. (Facultative Planktont). 



Cells 23-50 /* broad ; 6-10 /* thick. 



Blake (rr), Chain (r), Cochrane (r), Fishtrap (rr), Horse (r), Lac Court 

 Oreilles (rr), Little Bear (rr), Little Crooked (rrr), Loon (rr), Paddock (rrr), 

 Palmer (rrr), Rice (1) (rr), Tenderfoot (r), Tied Canoe (rrr), White Ash 

 (rr), Wolf (rr). 



In the second list of Wisconsin algae this alga was given as T. pro- 

 teiforme but I am now convinced that it is T. trigonum var. gractte. 

 The cells reach a much larger size than that given by Reinsch and the 

 excavation of the sides may be very much greater ; in fact the cells are 

 at times so delicate that they might be placed as Cerasterias species had 

 not other individuals in the same collection the ordinary cell shape of 

 T. trigonum var. gracile. 



TETRAEDRON MINIMUM (A. Braun) Hansgirg. PI. 24, Figs. 10-13. 

 Hedwigia 27: 131. 1888; G. S. West, Brit. Freshw. Algae 231, fig. 10lA. 1904. 



Cells small, flattened, front view square or oblong with slightly 

 rounded corners and concave sides. Side view fusiform-elliptic. Wall 

 smooth or finely granulate. Chloroplast single, parietal, with one 

 pyrenoid. (Facultative Planktont). 



Cells 6-20 IL long, 5-8 ^ thick. 



Beaver (2) (rrr), Camp (rr), Deer (rrr), Hillman (rrr), Horse (rr), Little 

 Bass (2) (rrr), Little Doctor (rr), Mendota (rrr), Okauchee (rrr), Paddock 

 (rrr), Round (3) (rrr). 



TETRAEDRON REGULARS Kiitzing. PI. 24, Fig. 14. 



Phycol. germanica 129. 1845. 



Polyedrium tetraedricum Nageli, Gatt. einz. Algen 84, pi. 4, figs. BSa-BSb. 

 1849. 



Cells medium sized, tetragonal, generally pyramidal, sides concave, 

 straight, or slightly convex. Angles with a single, heavy, short, blunt, 

 spine. ( Tychoplanktont) . 



Diam. cells (with spines) 14-45 p. 



Blake (rr). 



var. INCUS Teiling. PI. 24, Figs. 15-16. 



Sv. Bot. Tids. 6: 277, 274, fig. 12. 1912. 



Polyedrium regulare Chodat non Kiitzing, Mater, pour la flore crypt. Suisse 

 I 3 : 220, fig. 146. 1902. 



Cells small, tetragonal, flattened or pyramidal, sides slightly concave. 

 Angles produced into a single short delicate straight or curved spine. 

 ( Tychoplanktont) . 



