32 WISCONSIN PHYTOPLANKTON 



semicells semicircular and with lateral angles somewhat rounded, cell 

 outline crenulate. Vertical view narrowly elliptic but outlines of 

 sides smooth. Lateral view of semicells ovate. Cell wall with 3-5 

 rows of undulations within the crenae, the undulations forming con- 

 centric series ; central portion of wall smooth. Chloroplasts axial and 

 with two pyrenoids. 



Zygospores unknown. 



Cells 49-52 /a long ; 52-55 /* broad ; 17-19 jx broad at isthmus ; thick- 

 ness 26 /n (Lundell). 



Not found in the plankton of Wisconsin lakes. 



var. NoRDSTEDTiANUM (Reiusch) W. & G. S. West. PI. 57, Figs. 19-20. 



Monogr. Brit. Desm. 2: 146, pi. 58, fig. 12. 1905. 



Cosmarium Nordstedtianum Eeinsch, Contrib. ad Alg. et Fung. 89, pi. 10, figs. 

 nA-llB. 1875. 



Semicells with apices truncate and undulation of cell wall within 

 the crenae reduced in n\imber. (Tychoplanktont.) 



Cells 52 [I long, 47-51 /* broad ; breadth of isthmus 17 ju,. 

 Meta (rrr). 



The ornamentation of the cells as I have found it is similar to that 

 given by W. & G. S. West and not the scattered granules covering 

 the entire wall that Reinsch figures. 



7. Cosmarium amoenum De Brebisson. 

 in Ealfs, Brit. Desm. 102, pi. 17, figs. 3A-3C. 1848. 



Cells fairly small, length about twice the breadth, slightly con- 

 stricted, sinus open to sublinear, isthmus broad; semicells vertically 

 rectangular and with rounded apices. Vertical view broadly elliptic. 

 Lateral view of semicells narrowly oblong-elliptic. Cell wall granu- 

 late in outline and with face of cell bearing scattered granules in the 

 apical region and vertical rows of granules extending from apical 

 region to the semicell base, frequently with vertical pairs of granules 

 forming a transverse belt across the base of the semicell. Chloroplasts 

 axial and with two pyrenoids. 



Zygospores unknown. 



Cells 49 ju, long; 24 fi broad; 18 /x broad at isthmus (Ralfs). 



Not found in the plankton of Wisconsin lakes. 



var. mediolaeve Nordstedt. PI. 57, Fig. 21. 



Bot. Not. 1887: 160. 1887; Kgl. Sv. Vet.-Ak. Handl. 22, No. 8: 50, pi. 5, 

 fig. 12. 1888. 



Semicells with granules lacking in median area of front view and 

 with double row of granules at base of semicells prominent. (Tycho- 

 planktont. ) 



Cells 39 [i long ; 23 p. broad ; 15 fi broad at isthmus. 



Speese (rr). 



