108 



WISCONSIN PHYTOPLANKTON 



with three emarginate verrucae and a truncate projection in the 

 median portion, poles continued in straight processes with smooth 

 margins and a median row of spines. (Facultative planktont.) 



Zygospores unknown. 



Cells 68-79 fi long with processes, 26-32 /x long without processes ; 

 breadth with processes 81-89 [x, without processes 19-21 [i ; breadth 

 at isthmus 9-10.5 ju, ; thickness 15 ju,. 



Little Doctor (r). 



The species resembles S. natator W. West in the truncate projec- 

 tion on the face of the middle of the semicell but differs in the angle 

 of divergence of the processes as well as the shape and ornamentation 

 of the semicells. It is given the name iirinator because of the re- 

 semblance of a side view to a diver. 



44. Staurastrum subnudibrachiatum "W. & G. S. West, 



Trans. Roy. Soc. Edinburgh 41: 502, pi. 7, figs. 18-19. 1905. 



Cells small, breadth (with processes) about one and a half times 

 the length, slightly constricted, sinus widely open and with a blunt 

 apex, isthmus fairly broad; semicells subspherical, with the upper 

 portion continued in smooth gradually attenuated processes that ter- 

 minate in two blunt teeth, ends of processes at times obtuse and 

 entire, processes slightly divergent. Vertical view four or five 

 radiate, with the processes of one semicell alternating with those of 

 the other semicell, processes slightly attenuated and with the length 

 about equal to the diameter of the cell; body of the cells gradually 

 fusing with the processes, margin of cell retuse between the bases of 

 the processes. Cell wall without ornamentation. Cells generally 

 enclosed in a wide gelatinous envelope. 



Zygospores unknown. 



Cells 40-44 fi long with processes, 31-37 /x long without processes ; 

 breadth with processes 53-60 /x, without processes 20-22 /x; breadth 

 at isthmus 15-15.5 /. (W. & G. S. West). 



Not found in the plankton of Wisconsin lakes. 



var. incisum var. nov. PI. 80, Figs. 1-4. 



Cells smaller than the type, length (without processes) about one 

 and a half times the breadth, median constriction very slight; semi- 

 cells subspherical-quadrangular, with the processes arising abruptly 

 from the body of the semicell; processes of one semicell opposite 

 those of the other semicell, processes with parallel sides and deeply 

 bifurcate apices, the bifurcations tending to lie in the vertical plane 

 of the cell, furcations with rounded ends. Vertical view always 

 tetragonal, with the body of the cell circular and the transition from 

 process to body abrupt. Chloroplast axial, massive, with two long 

 plate-like extensions running into each process, frequently with a 

 plate entering each branch of the end of the process; pyrenoids 

 single and central. Cells imbedded in a copious spherical gelatinous 

 envelope. (Euplanktont.) 



