WISCONSIN PHYTOPLANKTON 139 



feature that there can be no doubt of the identity of the Wisconsin alga 

 with his species. 



Quadrigula lacustris (Chodat) comb. nov. PI. 33, Figs. 4^6. 



Raphidium Braunii var. lacustre Chodat, Bull. Herb. Boiss. 5: pi. 11, figs. 

 9-10. 1897; Mater, pour la fl. crypt. Suisse I 3 : 200, fig. 117. 1902. 



AnTcistrodesmus lacustre (Chodat) Ostenfeld, Hedwigia 46: 384. 1907. 



Cells spindle-shaped, straight, with pointed ends. Cells rarely soli- 

 tary, generally irregularly distributed throughout, or in groups with 

 their long axes parallel to the long axis of the fusiform gelatinous 

 colonial envelope. Chloroplast single, parietal, laminate, at one side 

 of the cell or spirally twisted; generally with a single pyrenoid. (Eu- 

 planktont). 



Cells 3-5 fi broad, 20-25 /* long. 



Blue Gill (rr), Browns (rr), Clear Crooked (cc), Green (2) (rr), Horseshoe 

 (1) (rr), Lynx (rr), Pokegama (2) (rr), Round (1) (rrr). 



ELAKTOTHRIX Wille 1898. 



Cells fusiform when mature, longitudinally arranged in pairs within 

 a fusiform homogeneous gelatinous matrix. Chloroplast single, laminate, 

 parietal, with one or two pyrenoids. Colonies epiphytic when young 

 and free-floating when mature ; or free-floating throughout the life of 

 the plant. 



Reproduction by a transverse division into two daughter cells which 

 remain unchanged for some time. Akinetes known. 



Wille first placed the alga as a close relative of Actinastrum Hantz- 

 schi Lagerheim, but later thought it a relative of Coccomyxa Schmidle 

 (Wille, in Engler & Prantl, Nat. Pflanzenfam. I 2 (Nachtr.) : 36, figs. 

 18A-18E. 1909) ; Pascher (Susswasserfl. Deutschl., Osterr. u. d. Schw. 

 5 2 : 220, figs. 25-26. 1915) places it among the algae of doubtful sys- 

 tematic position; while G. S. West (Algae 1: 202. 1916) thinks it 

 closely allied to Ankistrodesmus, a view which seems to me most logical 

 since Ankistrodesmus, Quadrigula and Elaktothrix form a very natural 

 evolutionary series. 



KEY TO THE SPECIES. 



Both poles of cells acute E. VIRIDIS 



One pole of cell acute, the other generally rounded E. GELATINOSA 



ELAKTOTHRIX GELATINOSA Wille. PI. 34, Figs. 1-3. 



Biol. Cent. 18: 302. 1898; in Engler & Prantl, Nat. Pflanzenfam. 1 s (Nachtr.) : 

 3G, figs. 18A-18E. 1909; W. & G. S. West, The Naturalist, 19O9: 2-91, figs. GA-SD. 

 1909. 



Colonies free-floating, elongate fusiform to somewhat irregular ; with 



