HOLOTRICHA 551 



E. actiniae A. (Fig. 251, c). About 155m long; in gastrovascular 

 cavity of Sagartia parasitica. 



Genus Monochilum Schewiakoff. Ovoid to ellipsoid; medium 

 large; uniform and dense ciliation in rows; oblong cytostome left 

 of median line, in about 1/4 the body length from anterior end; 

 short cytopharynx conical, with an undulating membrane; con- 

 tractile vacuole near middle , in fresh water. 



M. frontatum S. (Fig. 251, d). Anterior end broader; ventrally 

 flattened, dorsally somewhat convex; macronucleus ellipsoid; a 

 micronucleus ; feeds on algae; 80/x by 30^. 



Genus Dichilum Schewiakoff. Similar to Monochilum; but 

 membrane on both edges of the cytostome; in fresh or salt water. 



D. cuneiforme S. (Fig. 251, e). Ellipsoid; cytostome about 1/5 

 the body length from anterior end; right membrane larger than 

 left; small cytopharynx; macronucleus ellipsoid; about 40/i by 

 24/x; in fresh water. 



Genus Loxocephalus Eberhard. Ovoid to cylindrical; often 

 compressed; crescentic cytostome on slightly flattened area near 

 anterior end, with 2 membranes; often a zone of cilia around 

 body; usually 1 or more long caudal setae; endoplasm granulated, 

 yellowish to dark brown; macronucleus ovoid; a single contractile 

 vacuole; in fresh or brackish water. Many species. 



L. plagius (Stokes) (Fig. 251, /). 50-65^ long; nearly cyhndrical; 

 15-16 cihary rows; endoplasm usually darkly colored; in fresh 

 water among decaying vegetation. 



Genus Balanonema Kahl. Similar to Loxocephalus; but with 

 plug-like ends; cytostome difficult to see; a caudal seta; macro- 

 nucleus oval; contractile vacuole; ciliation uniform or broken in 

 the middle zone; fresh water. 



B. biceps (Penard) (Fig. 251, ^f). Ellipsoid; no ciha in the middle 

 region; contractile vacuole central; macronucleus posterior to it; 

 42-50m long. 



Genus Platynematum Kahl. Ovoid or elHpsoid; highly flattened; 

 with a long caudal seta; contractile vacuole posterior-right; small 

 cytostome more or less toward right side, with 2 outer mem- 

 branes; ciliary furrows horseshoe-shaped; in fresh or salt water. 



P. sociale (Penard) (Fig. 251, h). Anterior half more flattened; 

 ventral side concave; cytostome in the anterior third; yellowish 

 and granulated; 30-50iU long; sapropelic in fresh and brackish 

 water. 



