. In decaying algae.

It was this form, I believe, that Peck '95 described as a "ciliate."

[Illustration: Fig. 41.--_Pleuronema setigera_.]

Genus LEMBUS Cohn '66.

(Cohn '66; Quennerstedt '69; Kent '81; Fabre-Domergue '85; Gourret &
Roeser '88; Buetschli '88; Shevyakov '96.)

Free-swimming animals of elongate form, more or less elastic, and
flexible, bending readily to avoid obstacles, etc. The anterior half
is usually drawn out into a slightly curved neck-like portion. The
peristome is a small groove leading from the anterior end to the
mouth about midway down the ventral side of the body. Buetschli,
following Quennerstedt, describes an undulating membrane on each side
of the peristome groove. Other observers, however, usually describe
but one, the left, which is clearly defined and stretches out some
distance from the body, while the right border is described as having
smaller but very active cilia. The general body surface is clothed
with fine, uniform cilia, and body striae are usually absent. One
or more caudal bristles may be present. The contractile vacuole is
posterior and terminal, and may be multiple. The macronucleus is
spherical and perhaps double (Kent). Food is chiefly bacteria, and
the animals are frequently found with the anterior end embedded in
zoogloea masses. Salt water, usually in infusions.

Lembus infusionum, n. sp. Fig. 42.

The body is elongate, lancet-shaped, with a tapering anterior
extremity. The dorsal outline is concave through the bending of the
anterior end, while the ventral outline presents an even, convex
curve. The mouth lies slightly above the center of the body and marks
the posterior limit of the ventral peristomial groove, which curves
slightly from the anterior extremity. Each side of this groove bears
an undulating membrane, the left being much larger and conspicuously
striated. The general form of this left membrane is triangular,
the widest part is anterior, the narrowest at the mouth. The
right membrane is similar in form, but smaller and more active.
The endoplasm is colorless and finely granular, not regionally
differentiated. The ectoplasm consists of a relatively thick cortical
plasm specially noticeable in the posterior half of the body and
a delicate cuticle which bears almost imperceptible longitudinal
markings--the insertion points of the fine cilia. The body is covered
with uniform cilia except at the anterior extremity. Here they are
much larger and