_Chloramoeba_ Lagerheim; _Thaumatomastix_, Lauterborn. (ζ) Pellicle dense, tough or hard, often wrinkled or striate: contractile vacuole discharging by the flagellar pit. Nutrition variable 7. EUGLENACEAE _Euglena_ Ehrb.; _Astasia_ Duj. (Fig. 37, 3); _Anisonema_ Duj.; _Eutreptia_ Perty (Fig. 42, p. 124); _Trachelomonas_ Ehrb. (Fig. 37, 1); _Cryptoglena_ Ehrb. 2. Skeleton an open network of hollow siliceous spicules. Plastids yellow. Diameter under 500 µ. 8. SILICOFLAGELLATA _Dictyocha_ Ehrb. 3. Diameter over 500 µ. Mouth opening into a large reticulate endoplasm: flagella 1, or 2, very unequal. 9. CYSTOFLAGELLATA _Noctiluca_ Suriray (Fig. 48); _Leptodiscus_ R. Hertw. B. Fission oblique or transverse: flagella two, dissimilar, the one coiled round the base of the other or in a traverse groove; pellicle often dense, of numerous armour-like plates 10. DINOFLAGELLATA _Ceratium_ Schrank; _Gymnodinium_ Stein; _Peridinium_ Ehrb. (Fig. 46); _Pouchetia_ Schütt; _Pyrocystis_ Murray (Fig. 47); _Polykrikos_ Bütschli. The Protomastigaceae and Volvocaceae are so extensive as to require further subdivision. PROTOMASTIGACEAE I. Oral spots 2. Flagella distant in pairs. DISTOMATIDAE II. Oral spot 1 or 0. {111}A. Flagellum 1. (_a_) No anterior process: often parasitic OIKOMONADIDAE _Oikomonas_ K. (Figs. 37, 2, 8); _Trypanosoma_ Gruby (Fig. 39, _a-f_); _Treponema_ Vuill. (Fig. 39, _g-i_). (_b_) Anterior process unilateral or proboscidiform: cell often thecate BICOECIDAE _Bicoeca_ Clark; _Poteriodendron_ St. (_c_) Anterior process a funnel, surrounding the base of the flagellum: cells often thecate. (i.) Funnel free CRASPEDOMONADIDAE _Codosiga_ Clark; _Monosiga_ Cl.; _Polyoeca_ Kent; _Proterospongia_ Kent; _Salpingoeca_ Cl. (ii.) Funnel not emerging from the general gelatinous investment PHALANSTERIDAE B. Flagella 2, unequal or dissimilar in function, the one sometimes short and thick. (_a_) Both flagella directed forwards MONADIDAE _Monas_ St.; _Anthophysa_ Bory (Fig. 37, 13). (_b_) One flagellum, usually the longer, turned backwards BODONIDAE _Bodo_ St. (Fig. 38). C. Flagella 2, equal and similar AMPHIMONADIDAE _Amphimonas_ Duj.; _Diplomita_ K. (Fig. 37, 10); _Rhipidodendron_ St. (Fig. 37, 14). D. Flagella 3 TRIMASTIGIDAE _Dallingeria_ K. (Fig. 37, 6); _Costia_ Leclercq. E. Flagella 4 or more: mostly parasitic in Metazoa POLYMASTIGIDAE _Trichomonas_ Donne; _Tetramitus_ Perty (Fig. 37, 7); _Hexamitus_ Duj.; _Lamblia_ Blanchard. F. Flagella numerous, sometimes constituting a complete ciliiform investment, and occasionally accompanied by an undulating membrane: parasitic in Metazoa.