PHYTOMONADINA 225 



P. singularis D. (Fig. 98, i). lO-lifx by 8-9/^. 



Genus Pocillomonas Steinecke. Ovoid with broadly concave an- 

 terior end; covered with gelatinous substance with numerous small 

 projections; 6 flagella; chromatophores disc-shaped; 2 contractile 

 vacuoles anterior; nucleus central; starch bodies; without pyrenoid. 



P.flos aquae S. (Fig. 98, j, k). 13m by lOyu; fresh water pools. 



Family 6 Phacotidae Poche 



The shell typically composed of 2 valves; 2 flagella protrude from 

 anterior end; with stigma and chromatophores ; asexual reproduction 

 within the shell; valves may become separated from each other ow- 

 ing to an increase in gelatinous contents. 



Genus Phacotus Perty. Oval to circular in front view; lenticular 

 in profile; protoplasmic body does not fill dark-colored shell com- 

 pletely; flagella protrude through a foramen; asexual reproduction 

 into 2 to 8 individuals ; fresh water. 



P. lenticularis (Ehrenberg) (Fig. 98, I, m). 13-20/x in diameter; in 

 stagnant water. 



Genus Pteromonas Seligo. Body broadly winged in plane of suture 

 of 2 valves;. protoplasmic body fills shell; chromatophore cup- 

 shaped; one or more pyrenoids; stigma; 2 contractile vacuoles; 

 asexual reproduction into 2-4 individuals; sexual reproduction by 

 isogamy ; zygotes usually brown; fresh water. Several species. 



P. angulosa (Lemmermann) (Fig. 98, n). With a rounded wing 

 and 4 protoplasmic projections in profile; 13-17iu by 9-20ai; fresh 

 water. 



Genus Dysmorphococcus Takeda. Circular in front view; anterior 

 region narrowed; posterior end broad; shell distinctl,y flattened pos- 

 teriorly, ornamented by numerous pores; sutural ridge without 

 pores; 2 flagella; 2 contractile vacuoles; stigma, pyrenoid, cup-shaped 

 chromatophore; nucleus; multiplication by binary fission; fresh 

 water. 



D. variahilis T. (Fig. 98, o, p). Shell 14-1 9m by 13-17m; older shells 

 dark brown; fresh water; Maryland (Bold, 1938). 



Family 7 Volvocidae Ehrenberg 



An interesting group of colonial flagellates; individual similar to 

 Chlamydomonadidae, with 2 equally long flagella (one in Mastigo- 

 sphaera; 4 in Spondylomorum) , green chromatophores, pyrenoids, 

 stigma, and contractile vacuoles; body covered by a cellulose mem- 

 brane and not plastic; colony or coenobium is discoid or spherical; 

 exclusively freshwater inhabitants. 



