Fabre-Domergue '85; _P. coronata_ Kent '81; _Paramoecium chrysalis_
Ehr. '38; _Lembadion orale_ G. & R. '88; _Histiobalantium agile_
Stokes '85, '88.

The body is ovoid, slightly flattened, rounded at both ends, the
anterior end sharper than the posterior. The ventral surface is
almost entirely taken up by a peristome which extends from the
anterior end posteriorly three-quarters of the body length. The
posterior end of the peristome is straight, the left curved,
following the depressed portion. The body is covered with fine cilia
in longitudinal lines, except on the peristome. The mouth is small
and situated in the hollow of the peristome near the left border. On
the left peristome edge is a large undulating membrane. It begins
near the anterior end of the body and increases in height posteriorly
following the peristome edge around on the right side. This posterior
bend of the membrane causes the appearance of a full sail, so
often seen. It can be entirely withdrawn and folded together in
the peristome. On the right edge of the peristome are large,
powerful cilia. The contractile vacuole is central and dorsal; the
macronucleus is in the anterior half of the body, with one attached
micronucleus. Food consists of bacteria. Not very common. Fresh
and salt water. It often remains quiet, with membrane and cilia
outstretched, as though dead, but suddenly gives a spring and is
gone.


[Illustration: Fig. 40.--_Pleuronema chrysalis_.]


Pleuronema setigera, n. sp. Fig. 41.