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 bristle-like. I was unable to find any cilia in the
peristome. One long caudal bristle, one-quarter of the length of the
body, trails out behind. The macronucleus is spheroidal and placed
near the center of the body; a conspicuous micronucleus lies near it.
A row of contractile vacuoles extends from the posterior end. I have
seen as many as six of nearly equal size and one or two smaller ones.
The intervals of contraction are quite long. Length 70 to 75µ;
greatest diameter 10 to 12µ.

_L. infusionum_ resembles _L. elongatus_ in its general form and in
its mode of life, for it excavates a retreat in zoogloea masses and
lies there for considerable periods perfectly quiet. It differs
from _L. elongatus_ and from _L. velifer_ (probably the same as _L.
elongatus_ of Claparède & Lachmann) in the presence of the caudal
bristle, in the absence of annular markings, number of contractile
vacuoles, and in the slightly smaller size. It resembles _Lembus
verminus_ (Müller) as described by Kent (_Proboscella vermina_), and
_L. intermedius_ as described by Gourret & Roeser (_Lembus verminus_
syn.)in the absence of annular markings and in the presence of a