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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Key to families and marine genera of Heteromasligida. 
1. Two flagella nearly equal in size Family Bodonidse 
One main and 2 accessory flagella Family Trimastigidse 
Family Bodonidse: 
1. Body very plastic, almost amoeboid Genus *Bodo , p. 424 
Body not plastic; with large anterior cavity, holding flagella Genus * Oxyrrhis, p. 425 
Family Trimastigidse: 
1. With an undulatory membrane between accessory flagella Genus Trimastix 
Without such membrane; flagella contained in a ventral groove while at rest Genus Costia 
Key to marine genera of Polymastigida. 
1. Body flattened; ends rounded; sides hollowed; often with wing-like processes; cross section 
S-shaped Genus Trepomonas 
2. Body pyriform; one large asymmetrical groove; 4 flagella Genus Tetramitus 
3. Body spherical; many flagella equally distributed Genus Multicilia 
Key to families and marine genera of Euglenida. 
1. With deeply-insunk pharynx; no mouth 2 
With pharynx and distinct mouth Family Peranemidse 
2. Body plastic; usually with chromatopliores and eye-spot Family Euglenida: 
Body plastic; no chromatophores; no eye-spot Family Astasiidse 
Family Euglenidse: 
Body Euglena-Uke, inclosed in shell with round opening for exit of flagellum Genus Trachelomonas 
Family Astasiida :: 
Body with one flagellum Genus *Astasia, p. 425 
Family Peranemidse : 
1. Body striped; plastic; two diverse flagella Genus Heteronema 
2. Body striped; not plastic; posterior flagellum longer than the other Genus * Anisonema, p. 426 
3. Body striped; not plastic; with rod-like organ in pharynx Genus Entosiphon 
Genus MASTIGAMCEBA F. E. Schultze ’75. 
(Kent '81; Biitschli ’86; Klebs '92; Senn 1900.) 
In general the form is oval and either regular in outline or irregular through the presence of many 
pseudopodia. One flagellum usually quite large and distinct. Differentiation of ectoplasm and 
endoplasm distinct or wanting. One to several contractile vacuoles. The pseudopodia are occasionally 
withdrawn, and the flagellum is the sole means of locomotion. In some cases the flagellum turns into 
a pseudopodium, and, conversely, the pseudopodium at one end may become a flagellum (see below). 
In some rare cases the ectoplasm secretes a gelatinous mantle. Reproduction not observed. 
Fresh and salt water. 
Mastigamceba simplex, n. sp. Fig. 7. 
A very small form, first seen in the flagellated stage, aroused my interest bv reason of the fact 
that its flagellum lost its regular outline and became amoeboid, turning to a pseudopodium, while at 
the same time other pseudopodia were protruded from different parts of the periphery. In this con- 
dition ectoplasm and endoplasm could be made out with the clearest definition. After the pseudopodia 
were well formed, the body became flat and closely attached to the glass slide. In a short time one 
of the pseudopodia became longer than the rest; the body became more swollen; the pseudopodia were 
gradually drawn in, with the exception of the more elongate one; this became active in movement 
and finer in diameter, until ultimately it formed a single flagellum at the anterior of a small monadi- 
form flagellate. The process was repeated two or three times under my observation, so that I am 
convinced that it was not a developmental form of some rhizopod. Several of them were seen at 
different times during the summer, and they were always of the same size and form in the flagellated 
or amoeboid condition. I did not make out their reproduction, and I shall not be satisfied that this is 
a good species until their life history is known. 
In decaying algae. Length 10/<. 
