MARINE PROTOZOA FROM WOODS HOLE. 
445 
anterior end posteriorly three-quarters of the body length. The posterior end of the peristome is 
straight, the left curved, following the depressed portion. The body is covered with fine cilia in 
longitudinal lines, except on the peristome. The mouth is small and situated in the hollow of the 
peristome near the left border. On the left peristome edge is a large undulating membrane. It begins 
near the anterior end of the body and increases in height posteriorly following the peristome edge 
around on the right side. This posterior bend of the membrane causes the appearance of a full sail, 
so often seen. It can be entirely withdrawn and folded together in the peristome. On the right edge 
of the peristome are large, powerful cilia. The contractile vacuole is central and dorsal; the macro- 
nucleus is in the anterior half of the body, with one attached micronucleus. Food consists of bacteria. 
Not very common. Fresh and salt water. It often remains quiet, with membrane and cilia out- 
stretched, as though dead, but suddenly gives a spring and is gone. 
Pleuronema setigera, n. sp. Fig. 41. 
Body colorless, elongate, and with the general form of a cucumber, the posterior end being some- 
what pointed. The mouth and relatively small peristome are situated in the lower third of the body. 
The peristome begins as a shallow furrow at the center of the ventral surface and dips sharply into the 
buccal depression, which is deep and turned toward the posterior end. The left edge of the peristome 
bears a high undulating membrane, which extends anteriorly only as far as the center of the body; 
posteriorly it passes around to the right edge of the peristome, thus forming the characteristic mem- 
branous pocket. Inside the oral depression is a second undulating membrane, running down to the 
mouth. This is small and without an oesophagus. The body is clothed with long setose cilia which 
are frequently fully outstretched when the animal is resting, a slight tremor . of the large membrane 
alone indicating vitality. Posteriorly these appendages are drawn out into long filiform setse, the 
number varying in different individuals from three to nine or ten. These are extremely fine and 
difficult to see without a high power (e. g. T \- oil) and careful focussing of the substage condensor. 
Like P. chrysalis, the resting periods are terminated by sudden springs, otherwise the movements are 
steady and forward. The macronucleus is central, and the contractile vacuole posterior and terminal. 
Length 45/r to 50 /«; greatest diameter .17//. In decaying algse. 
It was this form, I believe, that Peck ’95 described as a “eiliate.” 
Genus LEMBUS Cohn ’66. 
(Cohn ’66; Quennerstedt ’69; Kent ’81; Fabre-Domergue ’85; Gourret & Roeser ’88; Biitschli ’88; Shevyakov ’96.) 
Free-swimming animals of elongate form, more or less elastic and flexible, bending readily to 
avoid obstacles, etc. The anterior half is usually drawn out into a slightly curved neck-like portion. 
The peristome is a small groove leading from the anterior end to the mouth about midway down the 
ventral side of the body. Biitschli, following Quennerstedt, describes an undulating membrane on 
each side of the peristome groove. Other observers, however, usually describe but one, the left, 
which is clearly defined and stretches out some distance from the body, while the right border is 
described as having smaller but very active cilia. The general body surface is clothed with fine, 
uniform cilia, and body strise are usually absent. One or more caudal bristles may be present. The 
