Synonyms: _Trichoda gibba_ Müller; _Oxytricha gibba_ Stein '59; _O. velox?_ Quen. '69; _O. kessleri_ Wrzes. '77. Body elongate, slightly sigmoid and swollen in the center, about 3-1/2 times as long as broad; the rounded anterior end is turned to the left, the similarly rounded posterior end to the right; both ends taper slightly. The peristome is long and narrow, with a distinct adoral zone which appears broken in its course. To the right of this adoral zone is a single line of preoral cilia. On the right border of the peristome is an undulating membrane. The three frontal cirri form a triangle and the five smaller anal cirri form a continuous line with the broken row of ventral cirri. There are two and one-half rows of ventral cirri and the marginal cirri are drawn in until they are ventral in position. Length 135µ; greatest width 40µ. [Illustration: Fig. 51.--_Amphisia kessleri_.] This variety differs from _O. kessleri_ as described by Wrzesniowski in having three frontal cirri instead of four. Another difference is in the structure of the nuclei and in their position. These differences are too minute to warrant a specific name. _O. velox_ of Quennerstedt is probably the same as _0. kessleri_, but differs in having three complete rows of ventral cirri. _O. velox_ has three frontal cirri in a line, thus differing from the Woods Hole form. KEY TO THE MARINE GENERA OF EUPLOTIDÆ. Diagnostic characters: Cilia, as well as the frontal, marginal, and ventral cirri, very much reduced; the anal cirri, on the other hand, are always present. The macronucleus is band-form. 1. Frontal cirri more than 8 2 Frontal cirri less than 8 3 2. Eleven marginal cirri on the left Genus _Certesia_ side; 11 frontal cirri Four marginal cirri, 2 on each Genus *_Euplotes_ side; 9 to 10 frontal cirri 3. Seven frontal, 5 anal, 3 right Genus *_Diophrys_ marginal, and 2 left marginal cirri No frontal, 5 anal, 3 right, Genus *_Uronychia_ and 2 left marginal cirri * Presence at Woods Hole indicated by asterisk. Genus EUPLOTES (Ehr. 1831) Stein '59. (Ehrenberg '31, '38; Stein '59; Cl. & Lach. '58; Quennerstedt '65, '67, '69; Bütschli '88; Kent '81; Gourret & Roeser '88; Möbius '88.)