DINOFLAGELLATA 257 



Family 7 Polykrikidae Kofoid and Swezey 



Two, 4, 8, or 16 individuals permanently joined; individuals 

 similar to Gymnodinium; sulcus however extending entire body 

 length; with nematocysts (Fig. 110, b); greenish to pink; nuclei 

 about 1/2 the number of individuals; holozoic; salt water. 



Genus Polykrikos Biitschli. With the above-mentioned char- 

 acters; salt or brackish water, 



P. kofoidi (Chatton) (Fig. 110, a, b). Greenish grey to rose; com- 

 posed of 2, 4, 8, or 16 individuals; with nematocysts; each nemato- 

 cyst possesses presumably a hollow thread, and discharges under 

 suitable stimulation its content; a binucleate colony composed of 4 

 individuals about UOm long; off California, 



P. barnegatensis Martin, Ovate, nearly circular in cross-section, 

 slightly concave ventrally; composed of 2 individuals; constriction 

 slight; beaded nucleus in center; annuli descending left spiral, dis- 

 placed twice their width; sulcus ends near anterior end; cytoplasm 

 colorless, with numerous oval, yellow-brown chromatophores; nem- 

 atocysts absent; 46^ by 31.5)u; 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. 261) 



Without annulus or sulcus Family 3 Phytodiniidae (p. 261) 



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 different 

 species; in many species certain plates drawn out into various proc- 

 esses, 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; hypotheca 

 often with short horns and epitheca drawn out; colorless, green, or 



