WISCONSIN PHYTOPLANKTON 43 



Micrasterias Kitchelii WoUe, Desm. U. S. 116, pi. 37, figs. 1-3, 1884; Saun- 

 ders, Proc. Washington Acad. Sci. 3: 408, pi. AA, fig. 23. 1901. 



Cells larger, sinus with extremities more open; polar lobe much 

 shorter; lateral lobes extending beyond the polar lobes and with 

 incisions deeper. (Tychoplanktont.) 



Cells 142 fi long ; 150 p. broad at basal lobes, 94 p. broad at apex of 

 polar lobe ; isthmus 20 p. broad. 



Tank (rrr). 



4. Micrasterias truncata (Corda) De Brebisson. PI. 60, Figs. 1-2. 



in Ralfs, Brit. Desm. 75, pi. 8, fig. 4; pi. 10, figs. 5A-5D. 1848; G. S. West, 

 Jour. Linn. See. Bot. 34: 383, pi. 9, figs. 9-16. 1899; W. & G. S. West, Monogr. 

 Brit. Desm. 2: 82, pi. 42, figs. 1-8; pi. 45, figs. 5-6. 1905. 



Cells relatively small, circular in outline and with poles flattened, 

 deeply constricted, sinus linear and with outer portion slightly open, 

 isthmus narrow; semicells five-lobed, polar incisions somewhat open, 

 comparatively shallow and with apex blunt; lateral incisions about 

 half the depth of the polar incisions and acute-angled to sublinear; 

 polar lobe broadly cuneate, with lateral margins widely divergent, 

 polar apex convex and without a median depression, polar angles 

 usuallj^ emarginate-bifid, rarely acuminate; lateral lobes asym- 

 metrical to symmetrical in shape, with a very shallow rounded incision 

 and the lobelets generally strongly emarginate. Cell wall smooth to 

 punctate. Vertical view elliptic, with poles acuminate. Lateral view 

 of semicells ovate-pyramidate. Chloroplasts with two prominent 

 vertical ridges and irregularly disposed accessory ridges; pyrenoids 

 5-10. (Facultative planktont.) 



Zygospores unknown. 



Cells 70-87 p. long ; 60-98 p broad at the base of semicell, 55-68 p 

 broad at apex of polar lobe ; isthmus 15-19 p broad. 



Beaverdam (rr), Chetek (rrr). Fish (rrr). Horseshoe (rrr), Sand (rrr). Soft 

 (sss), Speese (rrr). Tank (rrr). 



5. Micrasterias conferta Lundell. 



Nova Acta Eeg. Sci. Upsaliae 3 Ser. 8: 14, pi. 1, fig. 5. 1871; W. & G. S. West, 

 Monogr. Brit. Desm. 2: 88, pi. 43, figs. 4-8. 1905. 



Cells fairly small, with an elliptic outline, median constriction very 

 deep, sinus linear and with outer extremities overlapping to slightly 

 dilated, isthmus narrow; semicells five-lobed, with incisions forming 

 the polar lobes much deeper than those forming the lateral lobes, polar 

 incisions linear and outwardly curved, lateral incisions linear and 

 straight ; polar lobes obversely campanulate with bases narrow and 

 apices flaring, apical margin convex but with median portion emar- 

 ginate, apical margins with two erect spines near the angles and apical 

 emargination flanked on either side by a small mamillate projection 

 terminating in a short spine ; lateral lobules with two series of shallow 

 incisions, the ultimate lobules having their ends emarginate to slightly 

 bispinate. Cell wall smooth to finely punctate, without spines or other 



