in '41, Stein '67; _P. chrysalis_ Duj. '41, Fromentel
'74; _Cyrtostomum leucas_ Stein '67, Kent '81.

Form ovoid, elongate, occasionally a little flattened
dorso-ventrally. Mouth in the anterior third of the body. The left
edge of the mouth carries a distinct undulating membrane; the right
edge is plain, longitudinally striated and bears cilia. It is
slightly depressed and the depression is carried posteriorly in the
form of a shallow furrow which reaches to the posterior end. The
contractile vacuole is on the left side, the spheroidal nucleus on
the right side of the furrow. The body is uniformly covered with fine
cilia, and the periphery is uniformly studded with large trichocysts,
except along the furrow. Food consists of dinoflagellates and other
small forms. Color dark brown to black.

Length 330 mu; width 200 mu.

This form differs considerably from the fresh-water _Frontonia
leucas_ as described by Schewiakoff '89, especially in the extreme
length of the peristomial furrow, in the position of the nucleus and
contractile vacuole, and in the nature of the water canals. These
in the Woods Hole form are very irregular in size and very much
branched, not uniform as in Lieberkuehn's (see Buetschli) figure of
_Frontonia leucas_, nor radiating as in Schewiakoff's description.
This may be the same species as _Frontonia marina_, of Fabre-Domergue
'91, whose description and figure I have not seen.

[Illustration: Fig. 37.--_Frontonia Leucas_.]

Genus COLPIDIUM Stein '60

(Buetschli '88; Maupas '83.)

The general form is oval, slightly compressed laterally with the
dorsal side strongly arched. The ventral side is slightly incurved.
The anterior end is somewhat smaller than the posterior end, which is
broadly rounded. The mouth is placed some distance from the anterior
end in an oral depression and opens into a tubular oesophagus. There
are usually two undulating membranes which do not extend beyond the
mouth borders. The right undulating membrane extends down into the
oesophagus and appears to be attached to the walls of the latter. The
body stripes in front of the mouth are twisted to the left. The anus
is terminal and the contractile vacuole may be terminal or situated
forwards in the dorsal region. The macronucleus is spherical and
has one micronucleus attached. Food consists mainly of bacteria.
Movement rapid, but interrupted.

Fresh and salt water, common in infusions.

Colpidium colpoda Ehr., sp. Fi