Marine Protozoa from Woods Hole | Page 9

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, 21µ.
This species was observed by Peck '93.
[Illustration: Fig. 22.--Glenodinium cinctum.]
Genus PERIDINIUM Ehr. '32, Stein '83.
(Claparède & Lachmann '58; Bergh '81; Pouchet '83; '85; Gourret '88;
Bütschli '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.
Synonyms: Protoperidinium digitale Pouchet; Protoperidinium Bergh
p. p.; P. divergens Peck.
The shell is covered with pits of large size. The posterior part is

hemispherical and surmounted by a single horn or spine. The transverse
furrow is very oblique, and its two extremities are united by a sigmoid
longitudinal furrow. The anterior half bears two spines or horns of
different size, and variable. The nucleus is spherical or ellipsoidal and
placed in the posterior half of the shell.
Length 68µ; diameter 54µ. Common.
Although the description of Pouchet's P. digitale differs in some
respects from a careful description of the Woods Hole form, I think the
species are the same. The chief difference is in the single horn of the
posterior half; in Pouchet's form this is furrowed by a narrow groove
which runs to the S-shaped longitudinal furrow. In the Woods Hole
form I was unable to make out such a furrow. The flagella, also, were
not seen. This same form was pictured by Peck '95 as _P. divergens_.
[Illustration: Fig. 23.--Peridinium digitale.]
Peridinium divergens Ehr. Fig. 24.
Synonym: Ceratium divergens Kent.
The shell is spheroidal, widest centrally, attenuate and pointed
posteriorly; the anterior portion is armed with two short, pointed horns,
each of them having a toothed process at the basal portion of the inner
margin. They are frequently colorless and beautifully transparent, the
body being free from large opaque granules; again they are colored
brown or yellow. The nucleus is large and elongate and finely granular.
75µ long and 68µ in diameter. Common.
[Illustration: Fig. 24.--Ventral and dorsal aspects of _Peridinium
divergens_.]
Genus CERATIUM (Schrank).
(Stein '78; Perty '52; Clap & Lach. '58; Bergh '82; Pouchet '83; Gourret
& Roeser '88; Bütschli '85; Kent '81; Senn 1900; Schütt '98.)

The general shape is a flattened sphere with three long processes or
horns. The cross-furrow is either spiral or circular; the longitudinal
furrow is usually wide and occupies the greater part of the anterior half
of the shell. The shell is thick, reticulate or striped, and sometimes
provided with short spines; often distinctly porous. The anterior half is
composed of 3 equatorial and 3 apical plates, the latter being continued
into the horn-like process. The posterior half is composed of 3
equatorial and one apical plate continued into the posterior horn. The
right posterior plate is continued into a similar horn which may remain
rudimentary or be continued into a considerable process. Similarly the
left posterior horn is usually developed, but remains small. There may
be from 2 to 3, 4, and 5 horns. Chromatophores usually present, green
to yellow brown.
Fresh and salt water.
Ceratium tripos Ehr. Fig. 25.
The body is somewhat triangular and bears three horns, two of which
are shorter than the other one and slightly curved upward.
Length, including the horns, 290µ.
[Illustration: Fig. 25.--Ceratium tripos.]
Ceratium fusus Ehr. Fig. 26.
Synonym: Peridinium fusus Ehr.
The animal is very elongate, due to the presence of two long horns at
the extremities of the body. Color, yellow with chromatophores. Length
285µ; width 23µ.
Both of these species are common in the tow and in the algæ at the
edge of the wharf. Both of them are mentioned by Peck in '93 and '95.
[Illustration: Fig. 26.--Ceratium fusus.]
Genus AMPHIDINIUM Clap. & Lach.

The body is ovoid to globular and usually much flattened
dorso-ventrally. The anterior portion is very much reduced and is
somewhat head-like or cap-like. The longitudinal furrow extends
through the entire posterior