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 EUPLOTIDAE.

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; Buetschli '88; Kent '81; Gourret & Roeser '88; Moebius '88.)

Small to medium-sized forms. Rigid in form, colorless, or green by
chlorophyl. They are quite flat on the ventral surface but decidedly
arched dorsally, and the contour is usually oval. The anterior end is
broadly rounded to truncate; the posterior end is similarly rounded,
or may be somewhat pointed. The mouth is placed centrally or near
the left margin, and from it the right edge of the peristome forms a
curved line to the left, which bends forward, thus making the greater
part of the left edge the peristomial area. In front the peristome
bends sharply to the right and extends as far as the right end of the
adoral zone. Upon the frontal and median ventral surface are 9 to 10
great cirri (_Bauchwimpern_ of Stein). Posteriorly five great anal
cirri stretch out beyond the posterior body margin. In addition to
these there are two smaller marginal cirri upon the left body edge,
and two similar ones on the hinder part of the body. The dorsal
surface is rarely smooth, but usually is marked by longitudinal
ridges, and rows of dorsal bristles have been described. The single