WISCONSIN PHYTOPLANKTON 31 



var. PAPiLLATUM W. & G. S. West. PI. 57, Figs. 12-13. 

 Trans. Linn. Soc. 2nd. Ser. Bot. 5: 252, pi. 15, fig. 21. 1896. 



Cells much larger than the type and with sinus more open ; lateral 

 angles of semicells with a single long papilla, the papillae being de- 

 pressed towards the sinus. (Facultative planktont.) 



Cells 45-49 /t long; 33-37/* broad; 10-14 ju, broad at isthmus; 

 25 fjL in thickness. Length of papillae 1.5-2 fi. 



Devils (s). 



The cells of this variety that I have found in the plankton of 

 Devils Lake have the characteristic shape and inward pointing 

 papillae that W. & G. S. West show in their figure but their size is 

 somewhat smaller. 



In the plankton of Big Bass, Horseshoe and Shell lakes there was 

 an even smaller form with shorter papillae that were not depressed. 

 This has been given the form name minor (Trans. Wis. Acad. Sci., 

 Arts & Lett. 20: 345, pi. 10, figs. 2-5. 1922) but might well be con- 

 sidered a distinct variety. The front view of this form is indistin- 

 guishable from certain forms of Staurastrum brevispinum De 

 Brebisson so that the alga could be considered a compressed form of 

 this Staurastrum species. Since no triradiate forms of the alga were 

 found it has been relegated to Cosmarium instead of Staurastrum. 



The dimensions of the form minor are : length 31-38 /u, ; breadth 

 27-30 /x; breadth of isthmus 8.75-10 /x; thickness 17-25 /x. (PI. 57, 

 Figs. 14^17.) 



5. Cosmarium granatum De Brebisson. PI. 57, Fig. 18. 

 in Kalfs, Brit. Desm. 96, pi. 32, figs. 6A-6B. 1848. 



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

 deeply constricted, sinus linear, with apex slightly inflated and outer 

 margin open, isthmus narrow; semicells pyramidate and with apices 

 truncate, bases of lateral margins subparallel for a short distance 

 and then converging or broadly rounded, apical angles obtuse. Ver- 

 tical view elliptic. Lateral view ovate. Cell wall smooth to min- 

 utely punctate. Chloroplasts axial and with a single pyrenoid. 

 (Tychoplanktont.) 



Zygospores unknown. 



Cells 41 fi long ; greatest breadth of semicell 30 fi, breadth at apex 

 9 ju, ; breadth of isthmus 7.5 fx.. 



Trout (rrr). 



6. Cosmarium cyclicum Lundell. 

 Nova Acta Reg. Soc. Upsaliae 3 Ser., 8: 35, pi. 3, fig. 6. 1871. 



Cells of medium size, subcircular in outline, length and breadth 

 about equal, deeply constricted, sinus narrowly linear, with apex 

 slightly dilated and outer extremity somewhat open, isthmus narrow ; 



