No. 2.] FRESH-WATER PROTOZOA, 29 



Astasia Stein. 



Body elongated, spindle-formed, very flexible, spirally 

 striated or smooth. Mouth and pharynx evident, as in 

 Euglena. Close beside the large flagellum a very small 

 secondary flagellum. Nucleus and contractile vacuole 

 present. 

 As. sp. ( ?). Fig. yT,, is probably Astasia, although the sec- 

 ondary flagellum was not evident. 

 As. contorta (?) Duj., Fig. 103. 

 Sphenomonas Stein. 



Not flexible; body ellipsoidal with four strong keels, 

 giving the body a somewhat four-sided cross section. A 

 chief and a secondary flagellum and a pharynx present. 

 See Clostonema below. 

 Clostonema Stokes. 



Fusiform to elongate, not contractile. Two unequal 

 flagella, one carried forward and the other backward. 

 Pharynx present. Contractile vacuole double; anterior 

 nucleus central. 

 CI. socialis Stokes, Figs. 88 and 90. This is regarded by 

 Senn as belonging to the genus Sphenomonas of Stein, 

 but the absence of keels seems to separate the two, and I 

 have, therefore, retained Stokes' genus, Clostonema. 



SUB-ORDER HETEROMASTIGODA 



Key to Genera. 



1. Small animals sometimes showing amoeboid motions; 



no evident cuticle 2 



Larger and possessing a cuticle; body frequently 

 flattened 7 



2. Flagella two 3 



Flagella three Elvirea* 



3. Both flagella directed forwards Dinomonas^ 



* One flagellum directed backwards, trailing 4 



4. Anterior end oblique; mouth at base of flagella. . . . 



Phyllomitus* 



Body spiral Spiromonas* 



Body neither oblique or spiral 5 



