WISCONSIN PHYTOPLANKTON 29 



Lateral margins crenulate (6) C. cyclicwm 



Lateral margins granulate. 



Granules evenly distributed (8) C. Botrytis 



Granules restricted to margin and center. 



Central area not granulate (16) C. ovale 



Central area granulate. 



Many granules within margin (15) C. punctulatum 



Few granules with margin (14) C. quinariwn 



Cell apex rounded. 



Semicells not reniform. 



Sinus open, isthmus elongate (10) C. Portianwrn, 



Sinus linear (7) C. amoenum 



Semicells reniform (9) C. reniforme 



Apices of semicells elevated. 



Semicells distinctly three-lobed (13) C. protractum 



Semicalls not three-lobed. 



Apex of sinus widely inflated (12) C. commissurale 



Apex of sinus not widely inflated (11) C. ornatum 



1. CosMARiUM ciRCULARE Reinsch. PI. 57, Fig. 3. 

 Acta Soc. Senekenberg 6: 5, pi. 3, figs. C*-C*. 1867 (sep.) 



Cells fairly large, cell outline circular, deeply constricted, sinus 

 linear and with outer extremity somewhat inflated; semicells semi- 

 circular, with basal angles rounded. Vertical view narrowly elliptic. 

 Lateral view of semicells narrowly subcircular. Cell wall minutely 

 punctate. Chloroplasts axial and with two pyrenoids. (Tychoplank- 

 tont. ) 



Zygospores unknown. 



Cells 47.5 IX long ; 39 fx broad ; breadth of isthmus 15 [i. 



Cranberry (rrr). 



The cells observed were at the minimal dimensions usually given 

 for this species. 



2. CosMARiuM DEPRESSUM (Nagcli) Luudcll. PI. 57, Fig. 4. 



Nova Acta Eeg. Soc. Upsaliae 3 Ser., 8: 38. 1871. 



Cosmarium Seenedesmus Delponte, Mem. E. Accad. d. Sci. di Torino 2 Ser., 28: 

 101, pi. 7, figs. 28-34. 1877 (sep.). 



Cells slightly under medium size, breadth somewhat greater than 

 the length, very deeply constricted, sinus linear and with outer ex- 

 tremity expanded, isthmus very narrow ; semicells transversely elliptic 

 and with dorsal margin more broadly rounded than the ventral, 

 lateral margins broadly rounded. Vertical view elliptic. Lateral 

 view of semicells circular. Cell wall smooth. Chloroplasts with a 

 single pyrenoid. (Tychoplanktont.) 



Zygospores spherical, with a smooth wall (Delponte). 



Cells 38-51 [X. long ; 43-52 fi broad ; breadth of isthmus 7.5-9 [i. 



Fish (rrr). Fowler (rrr), Mercer (rrr), Nicaboyne (rrr), Oeonomowoc (rrr), 

 Okauchee (rrr), Sand (rrr). 



