34 WISCONSIN PHYTOPLANKTON 



Cells fairly small, length about one and a half times the breadth, 

 fairly deeply constricted, sinus a semicircular depression with a 

 rounded apex, isthmus elongate; semicells transversely elliptic and 

 with poles quite blunt, semicell outline granulate. Vertical view 

 broadly elliptic. Lateral view of semicells circular. Cell wall granu- 

 late, with conspicuous granules arranged in vertical series, at times 

 decussate. Chloroplasts axial and with one pyrenoid. (Tychoplank- 

 tont. ) 



Zygospores spherical, furnished with numerous short conical pro- 

 tuberances with rounded apices (De Bary). 



Cells 40 /A long ; 28 fi broad ; 10 /* broad at isthmus. 



Beaverdam (rrr). 



11. CosMARiuM ORNATUM Ralfs. PL 57, Fig. 25. 



Ann. & Mag. of Nat. Hist. 14: 392, pi. 11, figs. 3A-3C. 1844; W. & G. S. West, 

 Monogr. Brit. Desm. 3: 151, pi. 78, figs. 1-10. 1908. 



Cells small, length and breadth about equal, deeply constricted, 

 sinus linear, with apex slightly inflated and outer margin open, 

 isthmus fairly narrow ; semicells renif orm, with a broad truncate ele- 

 vation in the apical region, lateral margins broadly rounded, outline 

 of cells granulate. Vertical view elliptic, with poles broadly rounded 

 and central portion of sides somewhat inflated. Lateral view of semi- 

 cells subcircular and with a somewhat truncate apex. Cell wall with 

 granules within the margin (at times with granules in vertical 

 series) and with a transverse double row of granules below the trun- 

 cate portion of apex ; central area with a circular area of conspicuous 

 granules, face of semicell surrounding central area without granules. 

 Chloroplasts axial and with two pyrenoids. (Tychoplanktont.) 



Zygospores spherical, with numerous fairly long stout spines that 

 have conical bases and emarginate apices (W. & G. S. West). 



Cells 31 IX long ; 33 /u, broad ; 12.5 fi broad at isthmus. 



Zygospores 46-50 jm broad without spines, 70-95 /x with spines (W. 

 & G. S. West). 



Crooked (rrr), Muskallonge (rrr). 



12. CosMARiUM coMMissuRALE De Brebissou. 



in Meneghini, Linnaea 14: 220. 1840; Haifa, Brit. Desm. 105, pi. 16, figs. 8A-8D. 

 1848. 



Cells fairly small, breadth one and a half times the length, very 

 deeply constricted, sinus with inner portion rhomboidal, median por- 

 tion linear, and outer portion dilated, isthmus very narrow ; semicells 

 reniform, with lateral angles broadly rounded and apex truncate and 

 slightly elevated in the median portion. Vertical view elliptic and 

 with a conspicuous semicircular inflation in the median portion. 

 Lateral view of semicells broadly elliptic and with apex flattened. 

 Cell wall (in front view) with outline of truncate apex and lateral 

 angles granulate; median portion of cell face with a ring of granules 

 enclosing scattered granules or with a circular area in which all 



