HOW TO KNOW THE FRESH-WATER ALGAE 



364a (362) Cells strongly ilattened dorsiventrally; plates not evident; 



transverse furrow not completely encircling the cell. Fig. 260 .... 



HEMIDIN1UM 



Fig. 260. Hemidinium nasutum Stein, a, ven- 

 tral view; b, dorsal view. 



There are several species of this genus re- 

 ported from the United States. They are dif- 

 ferentiated by shape and size of cell and by 

 the pattern of the plates which are usually 

 very delicate and difficult of determination. 

 The cells are very much flattened when seen 

 from the side. 



Figure 260 



364b Cells not at all or but very little flattened dorsiventrally (nearly 

 round in cross section); plates evident (especially in empty cells); 



transverse furrow completely encircling the cell. Fig. 261 



GLENODINIUM 



Fig. 261. Glenodinium Kulczynski (Wolos.) 

 Schiller, a, ventral view showing longitudi- 

 nal furrow; b, dorsal view; c, apical view. 



The several species of this genus reported 

 from the United States are differentiated by 

 cell size and shape. The plate pattern is 

 much more easily discerned than in Hemidini- 

 um (Fig. 260) but patience is required in rotat- 

 ing the cell in order to determine this pattern. 

 As in other genera, especially Peridinium (Fig. 

 258) it is desirable to examine empty cells in 

 order to see the wall characters plainly. Most 

 species are globular or if flattened, not so 

 much as in Hemidinium. 



Figure 261 



365a (346) Colony mottle by flagella 366 



365b Colony non-motile, or if moving, by rhizopodial processes (pseudo- 

 podia) 370 



366a Colony globose or subglobose (oval); cells ovoid or pear-shaped, 

 compactly arranged or forming a hollow sphere 367 



366b Colony not globular; cells shaped otherwise 369 



153 



