12 



WISCONSIN PHYTOPLANKTON 



bluntly truncate. Cell wall yellow-brown, with apical portion a 

 deeper shade; without a median girdle, with numerous fine striae 

 extending to the cell apex. Chloroplast ridged (?), with an axial 

 row of 5-6 pyrenoids. 



Zygospores unknown. 



Length 317 /a; breadth 54 /A (Ralfs.) 



Not found in the plankton of Wisconsin lakes. 



Fig. 2, Closterium Ealfsii De Brebisson (x350). From a herbarium specimen in 

 the British Museum of Natural History collected by De Br6bisson. 



var. iiYBRiDUM Rabenhorst. PI. 53, Fig. 5. 



Kryptogamenfl. Sachs. Abt. 1: 174. 1863; W. & G. S. West, Monogr. Brit. Desm. 

 1: 183, pi. 24, figs. 8-13. 1904. 



Cells narrower than the foregoing and with inflation of the inner 

 margin less prominent. (Tychoplanktont.) 



Zygospores double; subovoid, with smooth walls (W. & G. S. West). 



Length 430 /x ; breadth in median portion 38 ft, at apices 9 /a ; 10 

 striae in 17.5 [x. 



Diameter of zygospores 51.5-80 ju. (W. & G. S. West). 



Found (rrr), Jag (rrr). 



9. Closterium Kuetzingii De Brebisson. PL 53, Fig. 6. 



Mem. d. 1. Soc. imp. d. Sc. nat. de Cherbourg 4: 156, pi. 2, fig. 40. 1856; Eaci- 

 borski, Sprawozd. Kom. fizyjogr. Akad. urn. w Krakowie 19: 8, pi. 1, fig. 2. 1884; 

 W. & G. S. West, Monogr. Brit. Desm. 1: 186, pi. 25, figs. 6-11. 1904. 



Cells long, of medium breadth ; straight, median portion naviculoid 

 and ends continued in processes with parallel sides and rounded 

 apices; terminal portion of processes somewhat curved. Cell wall 

 colorless to straw colored, without a median girdle but longitudina,lly 

 striated; striae delicate, 15-20 visible across face of cell, extending 

 to base of terminal processes. Chloroplast occupying striated portion 

 of cell, without longitudinal ridges, with an axial row of 4-6 pyre- 

 noids. Terminal vacuoles conspicuous. (Tychoplanktont.) 



Zygospores subrectangular, wath angles truncate and sides between 

 angles concave (Raciborski, W. & G. S. West). 



Cells 367-398 /x long ; 18-20 fi broad in median portion, 2.5 [i broad 

 at apices ; 10 striae in 10 [i. 



Greatest breadth of zygospore 48-51 /x, shortest breadth 35-36 /t 

 (W. & G. S. West). 



Carson (rrr), Crab (rrr), Meronk (rrr). 



