small forms. Color dark brown to black.

Length 330µ; width 200µ.

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 Lieberkühn's (see Bütschli) 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

(Bütschli '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