WISCONSIN PHYTOPLANKTON 69 



var. RETusuM Borge. PI. 67, Figs. 18-19, 



Bih. Kgl. Sv. Vet.-Ak. Handl. 19, Afd. 3, No. 5: 36, pi. 3, fig. 42. 1894. 

 Staurastrum brevispinum var. Boldtii forma retusum (Borge) W. & G. S, West, 

 Monogr. Brit. Desm. 4: 148, pi. 123, fig. 6. 1912. 



Cell shape as the foregoing but with the apices of semieells retuse 

 in the median portion. (Facultative planktont.) 



Cells 35-50 /x long; 38-40^ broad; isthmus 11-12 ^n broad. 



Beaverdam (r), Fish (rrr), Sishebogema (rrr). 



W. & G. S. West prefer placing the alga as a form of the variety 

 Boldtii but I think it more logical to follow Borge in considering it 

 a distinct variety. 



ft 



var. tumidum var. nov. PI. 67, Figs. 20-25. 



Length of semieells about one and a half times the breadth, sinus 

 widely open and acute-angled; semieells obsemicircular, with apices 

 tumid and subtruncate in the median portion. Vertical view of cells 

 triangular, with sides somewhat tumid (not retuse) and angles acute. 

 (Euplanktont?). 



Cells 42-52 im long ; 32-41 ^ broad ; breadth of isthmus 11-13 ix. 



Shell (ss). 



When the cells are viewed from above the variety is sharply differ- 

 entiated from the others of the species by the sharp angles and the 

 outward swelling of the sides of the cells. It is the only variety in 

 which the sides of the cells are not retuse. In the front view the pro- 

 portions are different, no other variety having a length of one and a 

 half times the breadth. 



5. Staurastrum pseudopachyrhynchum Wolle. PI. 68, Figs. 1-3. 



Desm, U. S. 125, pi. 51, figs. 32-35. 1884. 



Cells small, length about equal to the breadth, deeply constricted, 

 sinus open and with a broad rounded apex, isthmus elongate and 

 fairly narrow; semieells rhomboidal-elliptic, with the dorsal margin 

 convex and more tumid in the median region, lateral angles very 

 broadly rounded. Vertical view triangular, with the sides strongly 

 retuse and the angles broadly rounded. Cell wall smooth and of uni- 

 form thickness throughout. (Tychoplanktont.) 

 Zygospores unknown. 



Cells 32-34 /A long; 28-35 fi broad; isthmus 9-10.5 /x broad. 



Dummy (rr). 



The general shape of the cell is quite similar to ^S^. pachyrliynckum 

 Nordstedt but the cell wall does not have the thickening at the angles 

 so characteristically present in *S^, pachyrhynchum. All of the speci- 

 mens observed were triangular in vertical view. 



