WISCONSIN PHYTOPLANKTON 41 



Semicells with four lateral lobes. 

 Incisions of lateral lobea shallow. 



Polar incisions deep (5) M. conferta 



Polar incisions shallow (4) M. truncata 



Incisions of lateral lobes deep. 

 Cell outline oval. 



Lobes with more than one series of incisions. 

 Sides of incisions not undulate. 



Lobelets not deeply emarginate (6) M. denticulata 



Lobelets deeply emarginate. 



With a conical projection above the isthmus (9) M. Thomasiana 

 Without a conical projection above the isthmus (8) M. apiculata 



Sides of incisions undulate (7) M. radiosa 



Lobes with a single incision (11) M. radiata 



Cell outline quadrangular (10) M. Torreyi 



Polar lobe with accessory processes. 



Polar angles continued in long processes. 



Lateral processes in the same plane (13) Jf. Nordstedtiana 



Lateral processes not in the same plane (14) M. muricata 



Polar angles with short processes (12) M. americana 



Cells united in filaments (15) M. foliacea 



1. MiCRASTERiAs piNNATiTiDA (Kutzing) Ralfs. PI. 59, Figs. 1-2. 



Brit. Desm. 77, pi, 10, figs. 3A-3B. 1848; Johnson, Bot. Gaz. 19: 58, pi. 6, ^^r*. 

 5-6. 1894; W. & G. S. West, Monogr. Brit Desm. 2: 80, pi. 41, figs. 7-13. 1905. 



Cells small, breadth slightly greater than the length, deeply con- 

 stricted, sinus with apical portion linear and outer portion somewhat 

 open, isthmus narrow; semicells three-lobed, polar lobe with basal 

 portion subrectangular and with apical portion laterally expanded 

 and resembling the lateral lobes but smaller, ends of lateral expan- 

 sions bifid, polar lobe flattened to slightly convex; incisions between 

 polar lobes and lateral lobes very broad and with rounded apices; 

 lateral lobes horizontally disposed, lateral margins somewhat conver- 

 gent and apex bifid (rarely trifid). Cell wall smooth. Vertical view 

 narrowly elliptic, with poles drawn out and acuminate. Lateral view 

 of semicells ovate-pyramidate, with apices rounded. Chloroplast 

 extending into lateral lobes and lateral extensions of polar lobe, with 

 two prominent vertical ridges; pyrenoids usually three, one in each 

 lobe. (Tychoplanktont.) 



Zygospores spherical, with stout tapering spines that have rounded 

 apices (W. & G. S. West). 



Cells 54r-60 [i long ; 61-66 fi broad at the basal lobes, 45-50 ju, broad 

 at apex of polar lobes ; isthmus 10-12.5 fi broad. 



Kawaguesaga (rrr), Jenny (rrr), Lindy (rrr). 



Readily distinguished by the small size and the broad incisions 

 between the lobes. 



2. MiCRASTERiAS LATicEPS Nordstcdt. PI. 59, Fig. 3. 



Vidensk. Medd. f. d. naturhist. Foreri. i Kiobenhavn 1869: 220, pi. 2, fig. 14. 

 1870; Wolle, Desm. U. S. 115, pi. 37, figs. 4-5. 1884; Borge, Ark. for Botanik 1: 

 116, pi. 5, figs. 11-15. 1903. 



