WISCONSIN PHYTOPLANKTON 35 



Fig. 3. Cosmarium commissurale De Brebisson (x800). From a herbarium speci- 

 men in the British Museum of Natural History collected by De Brebisson at 

 Falaise, France. 



granules are irregularly distributed. Vertical view of wall with 

 transverse rows of granules at the poles and with central protuber- 

 ance granulate. Chloroplast axial and with one pyrenoid. 



Zygospores spherical, clothed with numerous long straight spines 

 with emarginate apices and conical bases (Ralfs). 



Cells 31 fi long ; 39 /i broad ; 8 fi broad at isthmus ; 21 /a in thickness. 



Not found in the plankton of Wisconsin lakes. 



var. CRASSUM Nordstedt. PI. 57, Fig. 26. 

 Vidensk. Medd. f. d. naturh. Foren. i Kiobenhavn 1869: 213, pi. 3, fig. 19. 1870. 



Breadth of cells one to one and a quarter times the length, inner 

 portion of sinus linear and not rhomboidal ; semicells elliptic in out- 

 line and with granulations more irregular. (Tychoplanktont.) 



Cells 32 /JL long ; 34 /x broad ; 9 ju, broad at isthmus. 



Travis (rrr). 



The relative proportions of the cells and the difference in siniis 

 and semicell shape distinguish the variety although there is, in gen- 

 eral, the same ornamentation as in the type. 



13. Cosmarium protractum (Nageli) De Bary. PI. 57, Fig. 27. 



Unters. u. d. Fam. d Conj. 72, 1858; W. & G. S. West, Monogr. Brit. Desm. 3: 

 181, pi. 82, fig. 8; pi. 94, figs. 4-5. 1908. 



Cells fairly small, length and breadth about equal, very deeply 

 constricted, sinus linear, with apex slightly inflated and outer portion 

 somewhat open, isthmus narrow; semicells reniform, with apices 

 considerably elevated and giving the semicells a three-lobed appear- 

 ance; lateral lobes broadly rounded; apical lobe truncate, with sides 

 subparallel and apex flattened, angles of lobes somewhat rounded, 

 cell outline granulate. Vertical view elliptic, with poles broadly 

 rounded and sides with a conspicuous median protuberance. Lateral 

 view of semicells ovate and with apices flattened. Cell wall with 

 coarse granules near the margins of lobes, at times with these granules 

 regularly arranged on the lateral lobes ; central area with similar 

 large granules arranged in concentric rings, wall between marginal 

 granules and central area granulate but granules considerably smaller. 

 Chloroplasts axial and with two pyrenoids. (Tychoplanktont.) 



