WISCONSIN PHYTOPLANKTON (37 



The few specimens found in our lakes have more rounded angles 

 than those from British lakes and they approach the variety parvum 

 W. West in shape but not in size. 



2. Staurastrum subgrande Borge. 



Arkiv for Botanik 15, No, 13; 46, pi. 4, fig. 9. 1918. 



Cells large, length 1.3-1.5 times the breadth, deeply constricted, 

 sinus widely open and acute-angled ; semicells transversely ovoid, 

 with the ventral margin more rounded than the dorsal ; lateral angles 

 broadly rounded and without ornamentation. Vertical view tri- 

 angular, with sides very slightly retuse and angles broadly rounded. 

 Cell wall smooth. 



Zygospores unknown. 



Cells 76-83 /x long ; 57-59 fx broad ; isthmus 18.5-20 fi broad (Borge) . 



Not found in the plankton of Wisconsin lakes. 



var. minor var. nov. PL 67, Figs. 10-12. 



Cells about half the size of the type and somewhat broader in pro- 

 portion to the length; dorsal margin of semicells much less rounded 

 than the ventral. (Facultative planktont.) 



Cells 36-40 /^ long ; 28-32 fx broad ; isthmus 8-9 fi broad. 



Devils (r). 



3. Staurastrum muticum De Brebisson. PI, 67, Figs. 13-15. 



in Meneghini, Linnaea 14: 228. 1840; Ralfs, Brit. Desm. 125, pi. 21, figs. 4A-4D; 

 pi. 34, fig. 13. 1848; W. & G, S. West, Monogr. Brit. Desm. 4: 133, pi. 118, 

 figs. 16-20. 1912, 



Cells small, length and breadth about equal, deeply constricted, 

 sinus open to sublinear, with an acute apex, isthmus narrow ; semi- 

 cells transversely elliptic, with the curvature of both margins the 

 same or with the dorsal margin more rounded than the ventral ; angles 

 of semicells broadly rounded. Vertical view triangular, with sides 

 markedly concave and angles broadly rounded. Cell wall smooth, 

 ( Tychoplanktont. ) 



Zygospores spherical, armed with stout, comparatively short spines 

 that are bifurcate at the distal end (De Brebisson), 



Cells 27 /x long ; 24-27,5 /x, broad ; isthmus 8,5 ju, broad. 



Diamond (rrr), 



W. & G. S, West state that "both triangular and quadrangular 

 vertical views are common" but I have observed only the triangular 

 individuals. It may be distinguished from all other smooth-walled 

 species without ornamentation by the size, the ratio between length 

 and breadth, and by the shape of the semicells. 



