WISCONSIN PHYTOPLANKTON 7 



wall and have deep notches that form rectangular teeth; pyrenoids 

 usually a single elongate rod in the axial portion of the chloroplast- 

 (Tychoplanktont. ) 



Zygospores spherical, with smooth thick walls (W. & G. S. West). 



Length 177-230 fj. ; breadth of median portion 48 /«. ; breadth at 

 apices 12.5-23 /t. 



Diameter of zygospores 73.6 /x ; thickness of zygospore wall 3.2 /x 

 (W. &G. S. West). 



Clear Crooked (rrr), Devils (1) (rrr), Devils (2) (rrr), Speese (rrr), Squirrel 

 (rrr). 



Exceedingly variable in size and relative proportions of length and 

 breadth. The striking axial chloroplast with notched longitudinal 

 rays is the most prominent feature of the alga. 



Penium De Brebisson 1844. 



Cells of variable length, length usually several times the breadth, 

 generally straight, with median portion somewhat constricted or 

 without a median constriction; sinus, when present, only a slight de- 

 pression. Cells not compressed, shape generally cylindrical, at times 

 fusiform to subelliptic, frequently somewhat attenuated at poles, 

 apices usually truncate and with rounded angles. Point of cell divi- 

 sion definite. Cell wall colorless to brownish, smooth to punctate or 

 granulate, at times with the granules arranged in definite longi- 

 tudinal series. Chloroplasts axial, with longitudinal radiating plates 

 that extend to the cell wall; pyrenoids generally in an axial row 

 at center of chloroplasts. 



Zygospores spherical to rectangular, walls usually smooth. 



KEY TO THE SPECIES. 



Cell wall with rows of granules (1) P. margaritaceum 



Cell wall without granules (2) P. minutum 



1. Penium MARGARITACEUM (Ehrenberg) De Brebisson, PI. 52, Fig. 6. 

 in Ralfs, Brit. Desm. 149, pi. 25, figs. lA-lC; pi. 33, fig. 3. 1848. 



Cells of medium size, length about ten times tlie breadth, slightly 

 constricted in median portion; cell shape cylindrical, with lateral 

 margins very slightly attenuated at poles and apices broadly rounded. 

 Cell wall with transverse lines at points of division ; ornamented with 

 vertical rows of minute granules, older portions of wall brownish. 

 Chloroplasts with a fairly massive axial portion from Avhich about 

 ten longitudinal ridges radiate to the cell walls ; pyrenoids fairly nu- 

 merous and forming an axial row in the central portion of chloroplast. 

 ( Tychoplanktont. ) 



Zygospores spherical, with smooth walls (Ralfs). 



Length 160 /«; maximum breadth 17.5/*; breadth at apices 10 ix. 



Diameter of zygospores 46 ju, (Ralfs). 



Lynx (rrr). 



