WISCONSIN PHYTOPLANKTON 53 



into the polar lobe and one or two ridges into each lateral lobe ; pyre- 

 noids more numerous in body of the cell than in lobes, 10-20 in each 

 chloroplast. (Tychoplanktont.) 



Zygospores unknown. 



Cells 125-140 /j, long ; greatest breadth 104-140 fi, breadth at apex 

 of polar lobe 54-72 ix ; breadth at isthmus 27-29 /x. 



Found (rr), Horseshoe (rrr), Howey (rrr), Thousand Islands (rrr). 



M. americana is subject to considerable variation in the length of 

 the polar processes and the depth of incision of the lateral lobes. 

 The granules of the cell body are always scattered, though they have 

 a tendency to be more numerous and more regularly arranged on the 

 portions bordering the incisions. The two prominent spines at the 

 bases of the polar incisions have not been pointed out by previous 

 investigators of the alga and my attention was first called to them by 

 Mr. Charles Bullard. I find that they are quite constant in all Amer- 

 ican specimens that I have examined, as well as in European speci- 

 mens in my herbarium. 



M. mahahuleshwarensis Hobson is quite like M. americana in the 

 asymmetrical processes of the polar lobes and the general cell shape 

 but differs in the lack of a lateral incision that divides the semicells 

 into five lobes. 



13. MiCRASTERIAS NORDSTEDTIANA Wollc. PI. 64, Fig. 3. 



Bull. Torr. Bot. CI. 11: 15. 1884; Desm. U. S. 113, pi. 52, figs. 3-5. 1884; 

 Johnson, Bull. Torr. Bot. CI. 22: 292 pi. 239, fig. 14. 1895; W. & G. S. West, 

 Trans. Linn. Soc. 2nd. Ser. Bot. 5: 239, pi. 14, fig. 4. 1896. 



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

 sinus somewhat open and with an acute apex, isthmus narrow ; semi- 

 cells five-lobed, polar incision widely open and with a rounded apex 

 that gives the polar lobe an exserted appearance ; polar lobe elongate, 

 with erect subparallel sides that bear on each side of the median 

 portion a simple mamiUate projection or a conical projection with 

 truncate ends that have short blunt teeth; upper angles of polar 

 lobe continued in very long, slightly divergent, tapering, cylindrical 

 processes that terminate in three minute blunt spines, polar apex 

 flattened and with a shallow emargination in the median portion, 

 apex with a second, considerably shorter, asymmetrically disposed, 

 pair of similar processes ; lateral processes separated by a blunt broad 

 incision, subhorizontally disposed, gradually tapering to blunt apices 

 that have three short divergent spines. Cell wall smooth or finely 

 punctate. Vertical view diamond-shaped, with poles continued in 

 straight cylindrical processes. Lateral view of semicells oblong, bases 

 with a round inflation and apices rectangular. (Tychoplanktont.) 



Zygospores unknown. 



Cells 203 ij. long ; greatest breadth 180 /a, breadth at apex of the 

 polar lobe 138 /x ; breadth at isthmus 28 fi. 



Diamond (rrr). 



