is rare, the macronucleus usually dividing at a late stage of cell
division. Length 30 to 50µ; width 15 to 20µ. Common in decomposing
algæ.


[Illustration: FIG. 39.--_Uronema marina_.]


KEY TO MARINE GENERA OF PLEURONEMIDÆ.

Diagnostic characters: The mouth is at the end of a long peristome
running along the ventral side; the body is dorso-ventrally or
laterally compressed. The entire left edge of the peristome is
provided with an undulating membrane which occasionally runs around
the posterior end of the peristome to form a "pocket" leading to
the mouth. The right edge of the peristome is provided with a
less-developed membrane. There may or may not be a well-developed
pharynx.

Body small; not produced into Genus *_Pleuronema_
neck-like elongation

Body medium-sized; anterior end Genus *_Lembus_
produced into neck-like elongation

* Presence at Woods Hole indicated by asterisk.


Genus PLEURONEMA Dujardin '41.