226. Plants filamentous and branched, slightly tapering toward the 



apices - - Phaeothamnion 



226. Plants not filamentous; usually motile, but many forms possess- 

 ing organs of locomotion existing in a sedentary state 227 



227. Plants unicellular; motile 228 



227. Plants multicellular or colonial; motile or non-motile 246 



228. Protoplasts inclosed by a lorica of various shapes (Pi. 98, Figs. 3-13), 

 with an opening for the organs of locomotion; most species 

 colonial, but some solitary^ 229 



228. Protoplast not inclosed by a lorica -— — - -233 



229. Lorica cone-shaped, narrowed posteriorly to a blunt or fine 



point 230 



229. Lorica some other shape, flask-like or pyramidal 231 



230. Lorica smooth, or with sUghtly undulate margins, not showing 

 transverse growth rings Dinobrtjon (in part) 



230. Lorica with marginal bristles marking successive stages of 

 growth Hyalobryon 



231. Loricas free-swimming, globose, with long spine-like outgrowths, 



with a narrow collar for a flagellum aperture Chrysostrella 



231. Lorica attached, usually not globose, without spines 232 



232. Lorica vase-shaped, transversely ovate or pyramidal, with a 

 wide base next to the substrate, a thread-hke pseudopodium 

 extended through an apical pore Lagynion 



232. Lorica narrowed in the basal portion^ protoplast with 2 flagella 



of equal length extending through an apical pore Derepyxis 



233. Cells free-swimming by means of a flagellum; wall impregnated 

 and covered by silicious scales of various shapes which bear 

 needles Mallomonas 



233. Cell walls without silicious scales 234 



234. Cells amoeboid, possessing long or short pseudopodia; proto- 

 plast weakly colored 2o5 



234. Cells not amoeboid; free-swimming by means of 2 flagella, or 

 sedentary; protoplast deeply pigmented 236 



235. Pseudopodia long and needle-like, not tapering from the 



]5ase - Rhizochrysis 



235. Pseudopodia short and tapering sharply from the base to a 



fine point Chrysamoeha 



236. Cells attached 237 



236. Cells free-swimming, or free-floating 238 



237. Cells tetrahedral; the angles tipped with 2 short spines Tetradinium 



237. Cells inversely pyramidal, the upper angles tipped with a 



single stout spine Raciborskia 



238. Cells lunate, or somewhat crescent-shaped, the horns produced 



to form a spine which is often recurved Cystodinium 



238. Cells not crescent-shaped 239 



239. Cells broadly ovate, or obovate, v^dth a truncate or bilobed an- 

 terior end; 2 anterior flagella; chromatophores 2 longitudinal bands.- 240 



239. Cells shaped otherwise; flagella not anterior.— 241 



240. Gullet present, extending posteriorly from bottom of apical 

 depression Cryptomonas 



240. Gullet absent Chroomonas 



^Cf. Dinobryon; species are differentiated by the shape of empty loricas. 



[589] 



