WISCONSIN PHYTOPLANKTON yi 



of spines within each margin, center with a ring of spines and a row 

 of spines leading to each angle or with the rows only and the ring 

 missing. (Euplanktont.) 



Cells 39-41 /A long ; breadth with spines 42-53 /i, without spines 

 35-40 fi ; isthmus 12-14 /x broad ; stout spines 5-7.5 /* long, slender 

 spines 3-7 fi long. 



Carroll (r). 



This might be considered a distinct species but the arrangement 

 of the spines and the two sizes of spines is that of S. setigerum. The 

 variety also differs in the quadrispinate endings of the angles of 

 the semicells. 



20. Staurastrum minnesotense WoUe. PI. 71, Figs. 14-15. 



Bull. Torr. Bot. CI. 12: 6, pi. 47, figs. 7-8. 1885; Freshw. Algae of U. S. 43, 

 pi. 57, figs. 7-8. 1887; W. & G. S. West, Trans, Linn. Soc. Bot. 2nd. Ser. 5: 260, 

 pi. 18, fig. 15. 1896. 



Cells large, length and breadth about equal, deeply constricted, sinus 

 widely open and with a more or less rounded apex, isthmus relatively 

 narrow; semicells broadly elliptic, generally with the dorsal margin 

 more tumid than the ventral, lateral angles each furnished with two 

 long stout divergent spines that lie in the same vertical plane; face 

 of the semicell with a second series of more delicate long spines, one 

 just inside of each angle and two just below the apex. Vertical view 

 triangular, with median portion of sides of the cells slightly retuse 

 to slightly tumid and the portion near the angles straight ; angles sub- 

 rectangular to obtuse, terminating in two long stout spines that lie 

 in the same vertical plane; each side of the cell with a single long 

 delicate spine perpendicular to the cell wall that lies on the margin 

 a short distance from the angle and with another similar intramar- 

 ginal spine within each spine at the margin. Cell wall coarsely punc- 

 tate. (Tychoplanktont.) 



Zygospores unknown. 



Cells 145 /x long with spines, 125 /x long without spines ; breadth of 

 cells with spines 172;u,, without spines 112 fi; isthmus 42.5 /a broad; 

 stout spines 25-32 n long, slender spines 25-28 fi long. 



Muskallonge (rr). 



This handsome Desmid cannot be confused with any other species. 

 It is the only one with spines of two sizes which has punctate walls 

 and anywhere near this size. The arrangement of the spines, particu- 

 larly in the vertical view, is also unique. W. & G. S. "West have called 

 attention to certain inaccuracies in the drawings of Wolle and my 

 observations on Wisconsin specimens confirm their statement that the 

 angles in a vertical view of the cell are not nearly so sharp as Wolle 

 shows them. There is some variation in the size and length of the 

 spines but the two terminal spines at the angles are always stouter 

 than the other four. Certain of the slender spines may also be lacking 



