42 WISCONSIN PHYTOPLANKTON 



Cells large, quadrangular, breadth somewhat greater than the 

 length, very deeply constricted, sinus with apical portion linear and 

 outer portion acute-angled, isthmus narrow; semicells three-lobed, 

 polar lobe transversely fusiform with apex rounded and lateral angles 

 very acute and slightly bent towards the base of the semicell ; lateral 

 lobes entire, horizontally disposed, lanceolate and with deeply bifid 

 apices. Cell wall minutely punctate. Vertical view fusiform, with 

 poles acuminate. Chloroplast completely filling the semicell, portion 

 in polar lobe entire, with two conspicuous vertical ridges extending 

 from the nucleus to the apex of the cell, with other ridges following 

 the outline of the cell; pyrenoids 12-15. (Tychoplanktont.) 



Zygospores unknown. 



Cells 140 /A long ; 196 fi broad at basal lobes, 185 /a broad at polar 

 lobe ; isthmus 26 ix broad. 



Crooked (rrr), Muskallonge (rrr). 



Borge has shown that this alga is subject to considerable variation 

 in the height of the lateral lobes and the degree of curvature of the 

 apex of the polar lobe. In view of this wide range of variation it 

 seems unwise to recognize the forms major and minor of Nordstedt. 



The alga should be compared with M. pinnatifida (Kutzing) Ralfs 

 and M. oscitans Ralfs. It differs from the former in the much greater 

 size and from the latter in the greater breadth of the polar lobe and 

 the narrower lateral lobes. 



3. MiCRASTERIAS DEPAUPEEATA Nordstcdt. 



Vidensk. Medd. f. d. naturhist. Foren i Kiobeuliavn 1869: 222 (with text fig.). 

 1870; Cushman, Bull. Terr. Bot. CI. 31: 395, text fig. 1. 1904; Borge, Arkiv for 

 Botanik 15, No. 13: 64, pi 5, figs. 16-17. 1919. 



Cells of medium size, length about a third greater than the breadth, 

 fairly deeply constricted, sinus sublinear and with outer portion some- 

 what open, isthmus narrow; semicells three-lobed, incision forming 

 lobes deep and very broadly rounded, polar lobe with a very broad 

 basal portion and upper portion somewhat expanded, polar apex con- 

 vex and slightly retuse in the median portion, angles of the polar 

 lobe deeply emarginate; basal lobes horizontally disposed, sub- 

 rectangular, with a shallow semicircular incision and the lobelets 

 deeply emarginate or the incision lacking and basal lobes with one 

 or two teeth. Cell wall punctate. Vertical view broadly fusiform. 

 Lateral view of semicells ovate. 



Zygospores unknown. 



Cells 81-104 jtt long ; 64-72 /x broad at basal lobes, 44-63 /x at apex 

 of polar lobes; isthmus 14r-16 /x broad; thickness up to 36 /x (Borge). 



Not found in the plankton of Wisconsin lakes. 



var. KiTCHELii (Wolle) W. & G. S. West. PI. 59, Fig. 4. 



Trans. Linn. Soc. 2nd. Ser. Bot. 5: 239. 1896; Cushman, Bull. Torr. Bot. CI. 31: 

 396, text fig. 2. 1904. 



