WISCONSIN PHYTOPLANKTON 73 



11. Staurastrum curvatum W. West. PI. 69, Figs. 4-9. 



Jour. Linn. Soc. Bot. 29: 172 pi. 22, fig. 13. 1892; W. & G. S. West, ibid. 35: 

 543, pi. 17, fig. 12. 1903. 



Cells of medium size, length (with spines) somewhat less than the 

 breadth, deeply constricted, sinus widely open and with apex very 

 blunt and rounded (semicircular), isthmus narrow, elongate and sub- 

 rectangular; semicells obversely subtriangular to sublunate, ventral 

 margins slightly convex, dorsal margins concave ; angles fairly sharp 

 and continued in long stout straight spines that taper to a sharp point, 

 spines strongly divergent. Vertical view triangular, sides of cells 

 retuse and angles acute; angles each bearing a long stout gradually 

 attenuated spine. Cell wall smooth. Chloroplast having a fairly 

 massive triangular central mass with two parallel laminate blades 

 running to each angle of the cell; pyrenoid single and central. 

 (Euplanktont.) 



Zj-gospores unknown. 



Cells 52-56 fx long with spines, 25-28 ju, long without spines ; breadth 

 64-80 [JL with spines, 28-38 jx without spines ; isthmus 7.5-8.5 p. broad ; 

 spines 21-25 /a long. 



Dummy (ss). 



Eesembling S. megacanthum Lundell but differing in the smaller 

 size of the body of the cell, the more divergent spines, and the rounded 

 apex of the sinus. 



var. elongatum var. nov. PL 69, Figs. 10-15. 



Cells with isthmus elongate and cylindrical; incurving of semicell 

 apices more pronounced. Vertical view with sides of the cell more 

 retuse. (Euplanktont.) 



Cells 40-50 [x long with spines, 25-29 ju, long without spines ; breadth 

 with spines 56-70 /<,, without spines 25-33 /x; isthmus 6-7 jm broad; 

 spines 17.5-25 fj. long. 



Blue Gill (rrr), Carroll (sss), Lindy (sss). 



This variety has an elongation of the isthmus that is comparable 

 to the elongation of the isthmus of S. cuspidatum De Brebisson. It is 

 readil}^ distinguished from S. cuspidatum by the side of the cells and 

 by the arrangement of the spines. The sides of the cells in a vertical 

 view of the variety are more incurved than those of the type and as 

 a result the body of the cell has a more delicate appearance. 



12. Staurastrum dejectum De Brebisson. PI. 68, Figs. 18-24. 



in MenegMui, Linnaea 14: 227. 1840; Kalfs, Brit. Desm. 121, pi. 20, figs. 5A-5M. 



1848. 



Cells fairly small, length (without spines) about equal to the 

 breadth, deeply constricted, sinus acute-angled and with the apex 



