furrow, producing a wing-like flange; longitudinal furrow broad in 

 the hypocone, extending into the epicone from the posterior pole; 

 rhomboidal plate broadly wedge-shaped, widest at the top and 

 reaching from the margin of the longitudinal furrow to just below 

 the anterior pole where there is not a true apex; epitheca with 14 

 plates, 7 precingulars, 3 apicals (median), 2 ventral apicals, 1 dorsal 

 apical, and a rhomboidal plate; hypotheca with the usual arrange- 

 ment of 5 postcingular and 2 large antapical plates; cell 49-55/x in 

 diameter, 50-70/a long. 



Plankter; in a variety of lakes; widely distributed but seldom 

 occurring in abundance. Wis. 



Peridinium wisconsinense Eddy 1930, p. 300 

 PI. 91, Figs. 13-15 



Cells large, spindle-shaped, slightly flattened dorsiventrally when 

 seen from the poles; epicone greatly produced to form a prominent 

 cone and the hypocone likewise produced to form a single, stout 

 sharply-pointed horn; transverse furrow broad, slightly spiral (in 

 our specimens, but described as strongly spiral), almost equally 

 dividing the cell into conical epi- and hypocones; longitudinal fur- 

 row extending from about half way to the posterior pole to the 

 transverse furrow but not into the epicone; rhomboidal cell ex- 

 tending from the top of the longitudinal furrow to the apical pole 

 which has a true apex; epitheca with 14 plates (including the rhom- 

 boidal), 1 median apical, 2 ventral apicals, 1 right lateral apical (on 

 the left as seen from the top), and 2 dorsal apicals; hypotheca with 

 5 postcingular and 2 antapical plates, one of which (left, as seen 

 from the posterior pole) forms the posterior horn; plates coarsely 

 reticulate; cells 48-56|u in diameter, 55-64/a long; cyst broadly ovoid 

 with one pole sharply and the other bluntly pointed, the membrane 

 thick and lamellate at the poles. 



Originally described from Lake Oconomowoc, Wisconsin. 



Common in a variety of lakes; frequently abundant in favorable 

 habitats. JVIich., Wis. 



FAMILY CERATIACEAE 



This family (erected for the genus Ceratium) has cells which 

 are fusiform in general outline. As described below, there is a 

 prominent apical horn in the epicone and 2-3 posterior horn-like 

 processes in the hypocone. The longitudinal sulcus is very broad 

 and short. The cell undergoes division in such a way that one of 

 the new protoplasts inherits 4 apical, 2 precingular and three post- 

 cingular plates, while the other portion retains the remaining 2 



[435] 



