WISCONSIN PHYTOPLANKTON 119 



Diam. cells (without spine) 13-18 /*; length of spines 7-8 //.. 

 Poor Farm (rr). 



This is probably what Chodat has figured as T. regulare. It differs 

 from the typical form in the smaller size, constantly concave sides of 

 the cell, and the delicate spines at the cell angles. 



var. TORSUM (Turner) Brunnthaler. PI. 24, Figs. 17-18. 

 in Pascher, Siisswasserfl. Deutschl., 6'sterr. u. d. Schw. 5": 150, fig. 169. 1915. 



Cells medium sized, tetragonal, with the two halves of the cells 

 cruciately arranged. Sides of cells straight or convex. Angles of cells 

 with a single short stout spine (Facultative Planktont). 



Diam. cells 25-40 p.. 



Horse (sss). 



Over a hundred individuals were observed in the plankton catch 

 from this lake and the twisting of the cell halves was a very constant 

 character. 



Tetraedron victorieae var. major var. nov. PI 24, Figs. 19-22; 



PI. 25, Fig. 1. 



Cells medium sized, four-sided, with two deeply emarginate sides 

 dividing the cell into two cruciately arranged halves. Sides of cells, 

 in vertical view, broadly fusiform with acute apices. All angles of 

 cells with a single heavy straight spine (Euplanktont). 



Cells (with spines) 30-60 /* long; 15-20 ^ broad. 



Chain (r). 



The cell shape and the peculiar twisting of the two halves is identical 

 with that of T. victorieae Woloszynska (Hedwigia 55: 203, pi. 6, figs. 

 1-4. 1914) which is known from the plankton of Lake Victoria 

 Nyanza, Africa. Measurement of about 25 Wisconsin individuals give 

 the following variation in size, length 30-60 p, breadth 15-20 ; whereas 

 the length of the African individuals varies from 20 to 30 /* and the 

 breadth 10-15 fi. 



TETRAEDRON VERRUCOSUM G. M. Smith. PI. 25, Figs. 2-3. 

 Trans. Wis. Acad. Sci., Arts, & Lett. 19 1 : 632, pi. 15, figs. 1-2. 1918. 



Cells large, tetragonal, pyramidate, or with the halves cruciate. Sides 

 convex. Angles of cell terminating in a very heavy, blunt spine. Cell 

 wall thick, verrucose. (Euplanktont). 



Diam. cells (with spines) 65-80 /*; length of spines 13-18 /*,. 



Bear (1) (rr). 



