of the two furrows. The endoplasm usually, but not always,
contains a bright red eye-spot.

Fresh and salt water.

Glenodinium compressa, n. sp. Fig. 21, a, b, c.

This species resembles _G. acuminata_ of Ehrenberg except that it is
strongly compressed laterally. The longitudinal furrow extends nearly
to the extremity of the animal. It begins as a narrow slit and widens
as it progresses upon the left side; it also becomes much deeper
on this side and at the bottom of the depression the longitudinal
flagellum is inserted. The transverse furrow runs evenly around the
body near the upper pole, giving to the shell almost the aspect of
an _Amphidinium_. Brown chromatophores may or may not be arranged
radially about a central amylum granule. One striking characteristic
is the depth of the two furrows. The nucleus is elongate and somewhat
curved; it lies against the posterior wall of the rather thick shell.
Not uncommon.

Length 40 mu; breadth 32 mu; width 18 mu.

The posterior end of the animal is often somewhat pointed and this
point frequently becomes attached, so that the animal whirls around
upon it as upon a pivot.

[Illustration: Fig. 21 a, b, c.--_Glenodinium compressa_, n. sp.]

Glenodinium cinctum Ehr. Fig. 22.

The body is globular, smooth, and homogeneous. Brown chromatophores
arranged radially, each in the form of a cone, the base of which
rests against the shell while the points turn inward. A bright-red
eye-spot may or may not be present; when present it is placed near
the junction of the two furrows. The longitudinal furrow is small.
Fresh water and salt.

Length and diameter the same, 21 mu.

This species was observed by Peck '93.

[Illustration: Fig. 22.--_Glenodinium cinctum_.]

Genus PERIDINIUM Ehr. '32, Stein '83.

(Claparede & Lachmann '58; Bergh '81; Pouchet '83; '85; Gourret '88;
Buetschli '86.)

The form is globular, ovoid or elongate, the apex frequently drawn
out into a long tube. The transverse and longitudinal furrows are
quite distinct, the former having often a spiral course about the
body. The two halves of the body are similar, the posterior being
somewhat shorter; the anterior half has seven equatorial plates, an
oral plate, two lateral apical plates, and one or two dorsal plates.
The two antapical plates frequently have a tooth-like process. The
bodies are colorless, green or brown.

Fresh and salt water.

Peridinium digitale Pouchet. Fig. 23.

Synony