EUCILIATA, HOLOTRICHIDA 355 



Chilodon cucullulus Miiller (Fig. 153, a). Length 100 to 300 

 microns. Fresh or salt water. 



Chilodon vorax Stokes (Fig. 153, h). Length about 200 

 microns. Fresh water among algae. 



Chilodon caudatus Stokes (Fig. 153, c). About 40 microns 

 long. In standing water. 



Chilodon fliiviatilis Stokes (Fig. 153, d). About 50 microns 

 long. Fresh water. 



Chilodon cyprini Moroff (Fig. 153, e). Body about 50 to 70 

 microns long by 30 to 40 microns broad. In the integument 

 and gills of the cyprinoid fishes. The organism, if freed from the 

 host skin, dies in from 12 to 24 hours. 



Genus Nassula Ehrenberg. Body large, oval to elongate, 

 flexible. Usually brightly colored. Often flattened dorso- 

 ventrally. The extremities are equally rounded. Cytostome 

 toward the left side. In some a poorly developed adoral zone 

 may occur. The cytopharynx is conspicuous by the presence of 

 a pharyngeal basket. Spherical macronucleus central. Con- 

 tractile vacuole one to several. Cysts are spherical. Fresh or 

 salt water. Several species. 



Nassula aurea Ehrenberg (Fig. 153, /). About 200 to 250 

 microns long. Fresh water. 



Nassula microstoma Cohn (Fig. 153, g). About 100 microns 

 long. Marine. 



Genus Opisthodon Stein. Body medium large, ovoid or pyri- 

 form. Dorsal surface convex, ventral flat. Cytostome located 

 at about one-fourth from the posterior end of body. Pharyngeal 

 basket is conspicuous. Two spherical macronuclei; one con- 

 tractile vacuole. Ciliation uniform. Fresh water. 



Opisthodon niemeccensis Stein (Fig. 153, h). Body about 200 

 microns long. In fresh water. 



Genus Orthodon Gruber. Body, oval, medium-large, con- 

 tractile and colorless. Much flattened; anterior end is curved 

 toward the left, while the posterior end rounded. Ventral side 

 is distinctly striated and ciliated. Dorsal surface is also finely 

 ciliated, although the striation is less distinct. Cytostome on 

 the right side margin. Cytopharynx with a conspicuous basket. 

 Oval macronucleus central; one contractile vacuole terminal. 

 Salt or fresh water. 



