[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