100 HANDBOOK OF PROTOZOOLOGY 



In many species, some of the plates are drawn out into various 

 processes, varying greatly in different seasons and localities 

 even among one and the same species. These processes seem to 

 retard the descending movement of the organisms from the 

 upper to the lower level in the ocean when the flagellar activity 

 ceases. The chromatophores are in the form of numerous small 

 platelets and yellow or green in color. In some deep-sea forms, 

 chromatophores do not occur. Chain formation by multiplica- 

 tion through fission occurs in some forms. Surface and pelagic 

 forms inhabiting fresh and salt waters. Several genera. 



Genus Peridinium Ehrenberg. Subspherical to ovoid; end- 

 view reniform. Annulus slightly spiral with projecting rims. 

 Often hypotheca with short horns and epitheca drawn out. 

 Colorless, green or brown ; stigma usually present. Cysts 

 spherical. Salt or fresh water. Numerous species. 



Peridinium tahulatum Claparede and Lachmann (Fig. 34, d). 

 Fresh water form. Diameter about 45 microns. 



Peridinium divergens (Ehrenberg) (Fig. 34, e). Salt water. 

 Color yellow. Diameter about 45 microns. 



Genus Ceratium Schrank. Body somewhat compressed; 

 with one anterior and one to four posterior horn-like processes. 

 Often large. Chromatophores are yellow, brown or greenish; 

 color variation is conspicuous even among the one and the 

 same species. Fission is said to take place at night and in the 

 early morning. Numerous species. Specific identification is 

 difficult due to a great variation. Fresh or salt water. 



Ceratium hirundinella Miiller (Fig. 34,/). Spinous projec- 

 tions on the shell. Seasonal and geographical variations. Chain- 

 formation frequent. Length 150 to 250 microns and breadth 

 40 to 80 microns. Fresh water. 



Genus Goniodoma Stein. Body polyhedral with a deep 

 annulus. Epitheca and hypotheca slightly unequal in size, com- 

 posed or regularly arranged armored plates. Chromatophores 

 small brown platelets. Marine. 



Goniodoma acuminatum (Ehrenberg) (Fig. 34, g). About 

 50 microns long. 



Family 2 Dinophysidae Stein and Bergh 

 The epitheca is flattened and smaller than the hypotheca. 



