WISCONSIN PHYTOPLANKTON 117 



TETRAEDRON TRIGONUM (Nageli) Hansgirg. PI. 23, Figs. 14-16. 



Hedwigia 27: 130. 1888. 



Polyedrium trigonum Nageli, Gatt. einz. Algen 84, pi. 4, figs. Bla-Blt>. 1849. 



Cells medium sized, triangular, flattened. Sides of cells generally 

 concave, rarely straight. Corners with a single, stout, straight or curved 

 spine. (Facultative Planktont). 



Diam. cells (without spines) 20-30 /*; length spines 8-10 /*. 



Crawling Stone (rrr), High (r), Pokegama (1) (rr), Rice (1) (rrr), Ten- 

 derfoot (rr), Tied Canoe (rrr). 



var. SETIGERUM (Archer) Lemmermann. PI. 24, Figs. 1-4. 



Arkiv. for Botanik 2, No. 2: 110. 1904. 



Tetrapedia setigera Archer, Quart. Jour. Micr. Sci. N. S. 12: 365, pi. 21, 

 figs. 14-17. 1872; Grevillea 1: 46, pi. 3, figs. 14-17. 1872; G. S. West, Brit. 

 Freshw. Algae 349. 1904; de Toni, Sylloge algarum 5: 113. 1907. 



Polyedrium trigonum var. setigerum (Archer) Schroder, Forschungsbr. a. d. 

 Biol. Stat. zu Plon 6: 23, pi. I, fig. 6. 1898. 



Cells small, triangular, flattened, with a conspicuous emargination 

 on each side in front view. Corners of cells rounded and produced into 

 a long delicately tapering spine. Chloroplast single, filling the entire 

 cell ; with one pyrenoid. (Facultative Planktont). 



Diam. cells (without spine) 7-9 /*.; length of spines 12-15 /*. 



White Ash (r). 



G. S. West and de Toni follow Archer in considering this organism 

 a member of the Myxophyceae West stating; "T. setigera Archer is a 

 beautiful little species known from N. W. Scotland and W. Ireland, 

 which has been erroneously referred by some authors to the chlorophy- 

 ceous genus Tetraedron. The cell contents of Tetrapedia setigera are 

 homogeneous and of a pale blue-green color." The cell contents of the 

 individuals that I have observed are distinctly grass green in color 

 and contain a single pyrenoid. This pyrenoid has not been noted 

 by either Archer or Schroder. Since the shape and dimensions of 

 the ce?.s that I have found are exactly the same as those given by 

 Archer I believe that I am dealing with the same organism that he 

 described and one which is a member of the Chlorophyceae and not 

 the Myxophyceae. 



var. GRACILE (Reinsch) de Toni. PI. 24, Figs. 5-9. 



Sylloge algarum 1: 598, 1889; Printz, Kgl. Norske Vidensk. Selsk. Skr. 1915, 

 No. 4: 29, pi. 3, figs. 167-169. 1916. 



Polyedrium trigonum var. gracile Reinsch, Die Algenfl. d. mitt. Th. v. 

 Franken 75: pi. 3, figs, la-lb. 1867. 



Tetraedron proteiforme G. M. Smith non (Turner) Brunnthaler, Trans. Wis. 

 Acad. Sci., Arts, & Lett. 19 1 : 632, pi. 15, figs. 4-5. 1918. 



