I 



PERITRICHIDA 395 



of Vorticella, but colonial; individuals are all alike. The 

 myonemes in the stalks are not continuous, and, therefore, in- 

 dividual stalks contract independently. The macronucleus is 

 a curved band; one contractile vacuole. Attached to animals 

 and plants. Some reach 4 mm. in height. Fresh or salt water. 



Carchesium polypinum Ehrenberg (Fig. 169, k). Ordinarily 

 in fresh, sometimes in salt, water. Body about 45 to 60 microns 

 long. 



Genus Zoothamnium Ehrenberg. Similar to Carchesium 

 except that the contractile myonemes of all stalks are con- 

 tinuous with one another, so that the entire colony contracts 

 or expands. Sometimes several millimeters high. Fresh or salt 

 water. 



Zoothamnium arhiiscula Ehrenberg (Fig. 169, /). In fresh 

 or salt water. Individuals about 60 microns long; colonies 

 often more than 6 mm. high. 



Genus Epistylis Ehrenberg. Body similar to that of Vorti- 

 cella, but usually in a dichtomous colonial form, resembling 

 superficially Carchesium; but the stalk not contractile. At- 

 tached to fresh or salt water animals. Colonies may reach 

 several millimeters in height. 



Epistylis plicatilis Ehrenberg (Fig. 170, a). Fresh water. 

 Body about 90 to 100 microns long. Colony often 3 mm. in 

 height. 



Epistylis flavicans Ehrenberg. On fresh water plants. Body 

 about 130 to 360 microns long. 



Genus Ophrydium Ehrenberg. Colonial. The whole is em- 

 bedded in a common mucilaginous mass. Stalk not contractile. 

 Fresh or salt water. 



Ophrydium sessile Kent (Fig. 170, b, c). Attached to fresh- 

 water plants. Body fully extended about 300 microns long. 

 Ovoid colony measures 5 mm. by 3 mm. 



Genus Opercularia Stein. The peristome end is oblique; 

 with an undulating membrane in the persitome. Short, not 

 contractile stalk branched and rigid. Fresh water. Several 

 species. 



Opercularia stenostoma Stein (Fig. 170, d). Fresh water; 

 often attached to Crustacea. When extended the body meas- 

 ures about 125 microns long. 



