446 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
contractile vacuole is posterior and terminal, and may be multiple. The macronucleus is spherical 
and perhaps double (Kent). Food is chiefly bacteria, and the animals are frequently found with the 
anterior end embedded in zoogloea masses. Salt water, usually in infusions. 
Lembus infusionum, n. sp. Fig. 42. 
The body is elongate, lancet-shaped, with a tapering anterior extremity. The dorsal outline is 
concave through the bending of the anterior end, while the ventral outline presents an even, convex 
curve. The mouth lies slightly above the center of the body and marks the posterior limit of the 
ventral peristomial groove, which curves 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 75//; greatest diameter 10 to 12 ju. 
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 Claparede & Laclnnann) 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 (Muller) 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 caudal bristle. It differs from the former, however, 
in the absence of a tentacle-like process, and from both in the absence of a double nucleus and in the 
presence of many vacuoles. These features are so characteristic of all the specimens examined that I 
have concluded, somewhat reluctantly, to give it a specific name. It is common in old infusions of 
alga;, especially after decomposition is well advanced. Its food consists of bacteria. 
Lembus pusillus Quennerstedt ’69. Fig. 43. 
Synonym: L. subulatus Kent ’81. 
This species is much smaller than the preceding, and might easily be mistaken for Uronema marina. 
It is subcylindrical in form, the anterior end bluntly pointed, the posterior end rounded. The oral 
apparatus is quite different from Uronema. The mouth, as in the preceding species, is at the end of a 
long peristomial groove extending from the anterior end to the middle of the body. The edges of the 
peristome bear undulating membranes as in L. infusionum. Like the latter, there is one caudal bristle, 
but unlike it there is only one posterior contractile vacuole, while the endoplasm is filled with large 
granules or food balls. The cuticle is distinctly striated with longitudinal markings, and the cilia are 
uniform in length. 
Habitat similar to that of L. infusionum , in zoogloea masses. Length 26 to 30/z ; diameter 7 to 8ju. 
