DINOFLAGELLATA 229 



tion slight; beaded nucleus in center; annuli descending left spiral, 

 displaced twice their width; sulcus ends near anterior end; cyto- 

 plasm colorless, with numerous oval, yellow-brown chromato- 

 phores; nematocysts absent; 46ju by 31.5ju; in brackish water of 

 Barnegat Bay. 



Tribe 2 Peridinioidae Poche 



The shell composed of epitheca, annulus and hypotheca, which 

 may be divided into numerous plates; body form variable. 



With annulus and sulcus 



Shell composed of plates; but no suture Family 1 Peridiniidae 



Breast plate divided by sagittal suture 



Family 2 Dinophysidae (p. 233) 



Without annulus or sulcus Family 3 Phj^todiniidae (p. 233) 



Family 1 Peridiniidae Kent 



Shell composed of numerous plates; annulus usually at equator, 

 covered by a plate known as cingulum ; variously sculptured and 

 finely perforated plates vary in shape and number among differ- 

 ent species; in many species certain plates drawn out into various 

 processes, varying greatly in different seasons and localities even 

 among one and the same species; these processes seem to retard 

 descending movement of organisms from upper to lower level in 

 water when flagellar activity ceases; chromatophores numerous, 

 small platelets, yellow or green; some deep-sea forms without 

 chromatophores; chain formation in some forms; mostly surface 

 and pelagic inhabitants in fresh or salt water. 



Genus Peridinium Ehrenberg. Subspherical to ovoid; reniform 

 in cross-section; annulus slightly spiral with projecting rims; hy- 

 potheca often with short horns and epitheca drawn out ; colorless, 

 green, or brown; stigma usually present; cysts spherical; salt or 

 fresh water. Numerous species. 



P. tahulatum Claparede et Lachmann (Fig. 104, c). 48m by 44^; 

 fresh water. 



P. divergens (E.) (Fig. 104, d). About 45m in diameter; yellow- 

 ish, salt water. 



Genus Ceratium Schrank. Body flattened; with one anterior 

 and 1-4 posterior horn-like processes; often large; chromato- 

 phores yellow, brown, or greenish; color variation conspicuous; 

 fission is said to take place at night and in the early morning; 



