24 WISCONSIN PHYTOPLANKTON 



1. Pleurotaenium Trabecula (Ehrenberg) Nageli. 



Gatt. einz. Algen 104, pi. 6, fig. A. 1849; W. & G. S. West, Monogr. Brit. Deam. 

 1: 209, pi. 30, figs. 11-13. 1904. 



Cells fairly large, length 11-15 times the breadth, median constric- 

 tion well defined; semicells cylindrical, very slightly attenuated to- 

 wards the poles, with a well defined basal inflation and a single 

 undulation above the basal inflation; apices truncate, with well 

 rounded angles, smooth and without tubercules. Cell wall punctate. 



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



Cells 390-664 fx long ; 26-46 jm broad at base of semicells, 16-32 ft at 

 apices. 



Zygospores 70 fi long; 48 fi broad (W. & G. S. West). 



Not found in the plankton of Wisconsin lakes. 



var. RECTUM (Delponte) W. & G. S. West. PI. 54, Fig. 1. 

 Monogr. Brit. Desm. 1: 212, pi. 30, figs. 9-10. 1904. 



Cells smaller, length generally proportionally greater; semicells 

 without undulations above the basal inflations. (Tychoplanktont.) 



Cells 284 fx long ; 20 ju. broad at base, 12.5 fx broad at apex ; isthmus 

 15 [I broad. 



Lindy (rrr). 



2. Pleurotaenium subcoronulatum (Turner) W. & G. S. West. 



Trans. Linn. Soc. 2nd. Ser. Bot. 5: 44, pi. 5, fig. 33. 1895. 



Docidium subcoronulatum Turner, Kgl. Sv. Vet.-Ak. Handl. 25, No. 5: 29, pi. 3, 

 fig. 1. 1893. 



Cells fairly large, length about 12 times the breadth, united to form 

 filaments, median constriction fairly well marked ; semicells cylindri- 

 cal, with bases inflated and lateral margins slightly undulate in the 

 lower third of the semicell, lateral margins very slightly attenuated 

 towards the apices ; apices dilated, truncate, with rounded angles and 

 a transverse ring of elliptic tubercules (about 10 visible in front 

 view of cell). Cell wall smooth or finely punctate. 



Zygospores unknown. 



Cells 407-453 ix long ; 29-37 ix broad at base of semicells, 25-29 fx 

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



Not found in the plankton of Wisconsin lakes. 



var. DETUM W. & G. S. West. PI. 54, Fig. 2-4. 



Trans. Linn. Soc. 2nd. Ser. Bot. 5: 235, pi. 13, figs. 2-3. 1896; G. S. West, Jour. 

 Linn. Soc. Bot. 38: 110. 1907. 



Cells with a distinct ligature-like constriction just below the apex 

 that gives the apex a distinctly dilated appearance. Cells united to 

 form filaments. (Facultative planktont.) 



Cells 385-567 /A long; 24-30 jn broad at base of semicells, 16-22 /ii 

 at apical constriction, 24-28 fx at apex (with tubercules) ; isthmus 

 23-24 fi broad. 



Bass (1) (rrr), Bass (3) (rrr), Diamond (rrr), Howe^ (sss). Red Bass (rrr). 



