442 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Key to marine genera of Chiliferidse. 
Diagnostic characters: Mouth never lies behind the middle of the body; the oesophagus is but slightly developed. The 
undulating membranes are placed either on the edge of the mouth or in the oesophagus. A peristomial depression leading 
to the mouth is absent or very slightly indicated. 
1. Mouth in the anterior half, undulating membrane on left edge only; right edge continued in a long 
ventral furrow Genus * Frontonia, p. 442 
2. Two undulating membranes; mouth central; no caudal bristles Genus * Colpidium, p. 443 
3. Two undulating membranes; caudal bristle Genus * Uronema , p. 443 
Genus FRONTONIA Ehr. (Cl. & Lach. ’581). 
(Ehrenberg, subgenus of liter saria ’38; Claparede & Lachmann ’58; Biitschli ’88; Shevyakov ’96.) 
Form elongate and cylindrical, or often flattened dorso-ventrally, with round or pointed ends. It 
is usually plastic and contractile. Cilia are evenly distributed about the body and are similar in length. 
The large, open mouth lies on the anterior half of the ventral surface, and is elongate and oval in out- 
line. On its left edge is a well-defined membrane which stretches across to the right side of the mouth. 
On the right edge is a small, longitudinally striped tract which is free from trichocysts and smooth in 
appearance. This tract is continued posteriorly in a long furrow, which in some cases reaches the pos- 
Fig. 39. — Uronema marina. 
terior end of the animal. A few rows of cilia in this furrow vibrate differently from the others and 
give the effect of a membrane (Biitschli). The oesophagus is extremely short and hard to make out. 
The body is usually covered uniformly with trichocysts, often of considerable size. There are 1 or 2 
vacuoles with long canals radiating throughout the endoplasm. The macronucleus is oval and cen- 
trally placed. Micronuclei vary from one to many. An anal opening is placed at the end of the long 
ventral furrow. The plasm is colorless or green by the presence of Zooehlorella, or colored brown or 
black by pigments. In these cases there is a considerable pigment mass on the anterior end. Move- 
ment is regular, forward, and combined with rotation. Food consists of foreign objects, diatoms, 
other protozoa and the like. Fresh and salt water. 
Frontonia leucas Ehr. Fig. 37. 
Synonyms: Frontonia vernalis Ehr. ’38; Bursaria leucas Allman ’55, Carter ’56; Panophrys leucas Duj. ’41, Stein ’67; 
Panophrys vernalis Dujardin ’41, Stein ’67; P. chrysalis Duj. ’41, Fromentel ’74; Cyrtostomum leucas Stein ’67, Kent ’81. 
Form ovoid, elongate, occasionally a little flattened dorso-ventrally. Mouth in the anterior third 
of the body. The left edge of the mouth carries a distinct undulating membrane; the right edge is 
plain, longitudinally striated and bears cilia. It is slightly depressed and the depression is carried 
posteriorly in the form of a shallow furrow which reaches to the posterior end. The contractile 
vacuole is on the left side, the spheroidal nucleus on the right side of the furrow. The body is uniformly 
