120 WISCONSIN PH7TOPLANKTON 



TETBAEDRON CAUDATUM (Corda) Hansgirg. PI. 25, Figs. 4-7. 

 Hedwlgia 27: 131. 1888; G. S. West, Brit. Freshw. Algae 231, fig. 101s. 1904. 



Cells small, flattened, five-sided; four of the sides concave and the 

 fifth deeply incised. Angles rounded and produced into a single 

 straight spine that lies parallel with the flat side of the cell. (Tycho- 

 planktont). 



Diam. cells 6-22 p, ; length of spines 1-3.5 /x.. 



Chain (rrr), East (rrr), Dutchmans (rrr), Horse (rr), Lake of the Woods 

 (rrr), Mendota (rrr), Palmer (rrr), Reserve (rrr), Wild Goose (rrr). 



The notch at one side of the cell varies considerably in depth but 

 is always deeper than the incurving of the other four sides. 



var. LONGISPINUM Lemmermann. PI. 25, Figs. 8-12. 



Bot. Cent. 76: 151. 1898; Forschungsbr. a. d. Biol. Stat. zu Ron 7: 117, pZ. 1, 

 figs. 8-9. 1899. 



Spines on corners at right angles to the flat side of the cell, generally 

 two pointing in one direction and three in the other. Spines much 

 longer than in the typical form. (Euplanktont). 



Diam. cells (without spines) 8-18 /*; length of spines 3-8 ^. 



Pine Tree (r), Travis (sss) 



This is a sharply defined variety, differing from the typical form in 

 the bending of the spines so that they lie at right angles to the plane 

 of the cell. Lemmermann 's figure 9 shows this very well but for some 

 reason the cell in his figure 8 has no spines and so is not at all charac- 

 teristic. 



TETRAEDRON PENTAEDRICUM W. & G. S. West. PI. 25, Figs. 13-17. 

 Trans. Linn. Soc. 2nd Ser. Bot. 5: 84, pi. 5, figs. 15-16. 1895. 



Cells small, five-cornered, with four corners in one plane and the fifth 

 lying at an angle of 30-90 degrees. Corners subacute, each with a 

 single, short, curved spine. Chloroplast single, parietal, with one pyre- 

 noid. (Facultative Planktont). 



Diam. cells (without spines) 5.5-14 /i, (with spines) 9-20 /*. 



Soft (rr). 



T. pentaedricum has not been observed since it was described from 

 Madagascar by the Wests. Chodat considers it a synonym of T. cau- 

 datum (Corda) Hansg. erroneously citing it as Tetrapedia pentaedri- 

 cum (Mater, pour la fl. crypt. Suisse 1 s : 219. 1902). Isolation of this 



