WISCONSIN PHYTOPLANKTON 9 



Poles sharply attenuated. 



Wall longitudinally striated. 



Poles truncate (8) CI. Balfsii 



Poles not truncate. 



Attenuated poles very narrow (9) CI. Kuetsingianum 



Attenuated poles fairly broad (10) CI. decorum 



Wall smooth. 



Apices rounded (5) CI. gracile 



Apices acute. 



Length at least 75 times the breadth (6) CI. aciculare 



Length less than 35 times the breadth (7) CI. acutum 



1. Closterium subtruncatum W. & G. S. West. PI, 52, Fig. 8. 



Jour. Linn. Soc. Bot. 33: 159, pi. 8, fig. 4. 1897; Borge, Ark. for Botanik 1: 78, 

 pi. 1, fig. 14. 1903. 



Cells of medium size, length 9-12 times the breadth, curvature mod- 

 erate, arc of curvature of outer margin about 65° ; inner margin con- 

 cave ; somewhat attenuated towards the poles which are broadly trun- 

 cate and slightly tumid in polar region of outer margin. Cell wall 

 slightly thicker at poles, colorless to brownish yellow; with a median 

 girdle and with numerous longitudinal striae. Chloroplast with an 

 axial row of about eight pyrenoids. (Tychoplanktont.) 



Zygospores unknown. 



Distance between apices 225-300 /i; breadth of median portion 

 20-26 fi ; about 12 striae in 10 /i. 



Clam (rrr), Fish (rrr). 



2. Closterium Venus Kiitzing. PI. 52, Fig. 9. 



Phycol. Germ. 130. 1845; Ealfs, Brit. Desm. 220, pi. 35, fig. 12. 1848; W. & G. S. 

 West, Monogr. Brit. Desm. 1: 137, pi. 15, figs. 15-20. 1904. 



Cells small, distance between apices 8-10 times the breadth; 

 strongly curved, the outer margin making an arc of 150°-165°, inner 

 margin with a curvature resembling that of the outer; gradually at- 

 tenuated to subacute apices. Cell wall colorless, rarely colored ; with- 

 out a median girdle; smooth. Terminal vacuoles large. (Tycho- 

 planktont.) 



Zygospores oblong, ends concave and sides tumid in median por- 

 tion; angles rounded; spore wall smooth. Halves of zygospore at 

 times cruciately twisted (W. & G. S. West). 



Distance between apices 70 ix ; breadth 8 fi. 



Length of zygospore 23-28.5 /i; breadth of zygospore 18-22 /n (W. 

 & G. S. West). 



Monona (rrr). 



3. Closterium moniliferum (Bory) Ehrenberg. PI. 52, Fig. 10. 



Die Infusionsthierchen 91, pi. 5, figs. 16'-16". 1838; Ralfs, Brit. Desm. 166, pL 28, 

 figs. 3A-3B. 1848; Lundell, Nova Acta Reg. Soc. Sci. Upsaliae, 3 Ser. 8: 80, 

 pi. 5, fig. 14. 1871. 



