great numbers, although it is less widely distributed than some other 

 species of Peridinium in our collections. Several of the described 

 varieties have been noted in our collections, but according to 

 Schiller (1935) these should be referred to the typical form and 

 the varietal names not retained. 



Plankter; found in several, especially soft water, lakes and in 

 desmid habitats. Wis. 



Peridinium limhatum (Stokes) Lemmermann 1900c, p. (120) 



PL 91, Figs. 16-18 



Cells ovate, the epicorie narrowed and produced to form a promi- 

 nent apiculation which is bifurcate and often turned to the left 

 when viewed from the ventral side; hypocone broad, with 2 stout 

 posterior horns; transverse furrow broad, slightly spiral, unsymmetri- 

 cally dividing the cell into a high epicone and a short hypocone; 

 longitudinal furrow very broad in the hypocone, extending from 

 the posterior pole to well within the epicone; rhomboid plate extend- 

 ing from the top of the longitudinal furrow to the apical pole, which 

 has a true apex and pore; epitheca with 10 plates; hypotheca with 

 5 ( ? ) postcingulars and 2 antapical plates ( these two produced to 

 form the posterior horns); sutures and transverse furrow striated; 

 plates reticulate; cells 60-65/x in diameter, 80-85.5/* long. 



Rare; in the plankton of soft water lakes and in Sphagnum bogs. 

 Wis. 



Peridinium pusillum (Penard) Lemmermann 190 Id, p. 65 



PI. 107, Figs. 7-9 



Cells ovoid, somewhat flattened dorsiventrally, the epicone 

 slightly longer than the hypocone so that the transverse furrow is 

 inframedian, and not spiral; epitheca slightly produced at the apex 

 and emarginate, with 7 precingular and 6 apical plates; hypotheca 

 with 5 postcingular and 2 antapical plates; chromatophores golden- 

 brown; 13-20/A in diameter, 18-24/a long. 



Mich. 



Peridinium Willei Huitfeld-Kaas 1900, p. 5 

 PI. 91, Figs. 22-25 



Cells large, subglobose, very little compressed dorsiventrally, 

 broadly rounded at both poles, with a wing-like flange which forms 

 a crest anteriorly and two lobes posteriorly, and with raised edges 

 along the margins of the sutures of the plates ( especially in mature 

 cells); transverse furrow broad, spiral, dividing the cell unsymme- 

 trically into a high epicone and a short hypocone, with a wide 

 border that often extends down along the edge of the longitudinal 



[434] 



