WISCONSIN PHYTOPLANKTON 17 



polar region dilated, with apex slightly tumid and angles rounded; 

 pole ornamented with a subapical whorl of conspicuous, conical, up- 

 wardly curved teeth (5 generally visible in front view of cell) that 

 do not extend beyond the apex. Cell wall smooth or punctate. Front 

 view with about four longitudinal, parietal, slightly undulate chloro- 

 plasts that contain numerous pyrenoids. (Tychoplanktont.) 



Zygospores unknown. 



Cells 337-410 /x long; 47.5-50 /i broad at inferior whorl, 37-42.5 /t 

 at superior whorl, 25-27.5 /i at apex (without spines) ; breadth 

 isthmus 30-32.5 /t. 



Little Doctor (rrr), Tank (rrr). 



Sharply differentiated from the other species by the whorls of 

 mamillate protuberances. 



6. Pleurotaenium Trochiscum W. & Cr. S. West. 



Trans. Linn. Soc. 2nd. Ser. Bot. 5: 235, pi. 13, jigs. 4-5. 1896; ibid. 6: 142, 

 pi. 19, figs. 7-8. 1902. 



Cells of medium size, length 10-16 times the breadth, constriction 

 well marked; semicells cylindrical, with sides slightly attenuated to- 

 wards the poles, basal inflation pronounced ; poles truncate, flattened, 

 with rectangular angles, and without polar tubercules. Cell wall 

 with 12-15 transverse rings of irregular to quadrangular areas where 

 the wall is not internally thickened; thin areas on basal inflation 

 much smaller and more irregular, thin areas of polar region irregu- 

 larly elongate. 



Zygospores unknown. 



Cells 265-468 p. long ; 20-42 /a broad at base of semicells, 21-29 fx at 

 apex. (W. & G. S. West.) 



Not found in the plankton of Wisconsin lakes. 



Var. tuberculatum var. nov. PI. 55, Fig. 3. 



Apices with a ring of conical to rounded tubercules (about 5 visible 

 in front view of cell). About 5 parietal, longitudinal, ribbon-like 

 chloroplasts with fairly smooth outline visible in front view; pyre- 

 noids numerous. (Tychoplanktont.) 



Cells 384-420 fi long ; 32-34 ix broad at base of semicells, 23-27.5 fi 

 at apex ; isthmus 24-26.5 /a broad. 



Little Doctor (rrr), Sunday (rrr). 



In the scanty material observed the apical tubercules so commonly 

 found in the genus were well defined. Since such careful investiga- 

 tors as W. & G. S. West have not described them it is evident that the 

 Wisconsin plants differ from the type and since this presence or 

 absence of apical tubercules is such an important feature of the 

 genus these cells are considered a distinct variety. 



DOCIDIUM De Brebisson 1844 (emend. Lundell 1871). 



Cells solitary, relatively small, straight, length several times the 

 breadth, cylindrical ; median constriction shallow, sinus always widely 

 open, isthmus breadth practically the same as the breadth of the cell ; 



