444 
BULLETIN OE THE UNITED STATES FISH COMMISSION. 
Uronema marina Duj. Fig. 39. 
Synonyms: Enchelys triquetra Dujardin; E. corrugata Duj.; Cryptochilum griseolwrn Maupas ’83; Philaster digitiformis 
Fabre-Domergue ’85. 
Small animals with ellipsoidal form and about twice as long as broad. The moutli lies in the upper 
half of the body and bears a well-developed undulating membrane upon its left edge. The membrane 
is longitudinally striped and covered with long and vibratile cilia. The right edge of the mouth bears 
cilia which are about the same in size as the body cilia, but are more closely inserted (Schewiakoff) . 
The most characteristic feature is the long caudal bristle, which is extremely delicate and about 
two-thirds the length of the body. Schewiakoff thinks this bristle has a sensory function. I could 
not make this out, for although other protozoa ran against this bristle, often bending it well over to 
one side, the animal shjwed no sign of irritability but lay quiescent. A spherical macronucleus with 
attached micronucleus lies in the center of the body. The contractile vacuole is posterior in front of 
the bristle. The macronucleus was found to be double, as though just divided, in a large percentage 
of cases. This may be a precocious division of the nucleus long before signs of the body division are 
evident. Such a phenomenon, however, is rare, the macronucleus usually dividing at a late stage of 
cell division. Length 30 to 50 ju; width 15 to 20 /<. Common in decomposing algse. 
Key to marine genera of Pleuronemidx. 
Diagnostic characters: The mouth is at the end o£ 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 neck-like elongation Genus * Pleuronema, p. 444 
Body medium-sized; anterior end produced into neck-like elongation Genus *Lembus, p. 445 
Genus PLEURONEMA Dujardin ’41. 
(Perty ’52; Clap. & Lach. ’58; Stein '59, vol. 1; Quennerstedt ’67; Kent ’81; Biitschli ’88; Schewiakoff ’89; Shevyakov ’96.) 
Small to medium-sized ciliates, with an unchanging form. They are somewhat lens-shape and 
laterally compressed, the two surfaces about equally arched. The ventral surface is nearly straight 
or but slightly arched; the dorsal is quite 
convex. The anterior and posterior ex- 
tremities are equally rounded. The per- 
istome begins as a small depression, but 
becomes larger until it takes in nearly 
all of the ventral surface. The depres- 
sion becomes much deeper at about the 
center of the body, and is especially 
marked on the left side of the peristome. 
In this deeper portion is the mouth, 
with an almost imperceptible oesophagus. 
Upon the left edge of the peristome is a 
high, undulating membrane, sail-like in 
appearance when extended. This may 
stretch around the posterior edge of the 
peristome and upon the right side, thus 
forming a pocket by means of which the 
food particles are directed into the mouth. The rest of the right edge of the peristome is occupied by 
closely approximated powerful cilia (Biitschli) or a second undulating membrane (Stein). The body 
cilia are relatively long. Trichocysts and caudal bristles may be present. The contractile vacuole is 
subterminal and dorsal; it is questionable whether there are canals leading to it. A round macro- 
nucleus with one micronucleus is in the anterior half of the body. The anus is terminal. Food is 
chiefly bacteria. Movement combines springing with swimming and rotation. Fresh and salt water. 
Pleuronema chrysalis Ehr., sp. Fig. 40. 
Synonyms: Pleuronema crassa Dujardin ’41; P. marina Duj. ’41; Fabre-Domergue ’85; P.coronata Kent ’81; Paramcccium 
chrysalis Ehr. ’38, Lembadion ovale G. & R. '88; Histiobalantium agile Stokes ’85, '88. 
The body is ovoid, slightly flattened, rounded at both ends, the anterior end sharper than the 
posterior. The ventral surface is almost entirely taken up by a peristome which extends from the 
