lOO DAVENPORT ACADEMY OF SCIENCES. 



tome about one-third the length of the body. Nuclei two. Con- 

 tractile vesicle single. 



OXYTRICHA PELLIONELLA Miill. 



Body elongate-elliptical, wider centrally and tapering toward 

 each extremity. The marginal setae are set well in on the ventral 

 surface. Three prominent frontal styles, and five anal styles aris- 

 ing near the posterior border and extending nearly their full length 

 beyond it, sometimes bent at their distal ends. 



Nuclei two, both posterior to the mouth. Contractile vesicle on 

 the left side near the posterior tip of the peristome. 



Length, 80-100 microns. (Fig. 167, PI. XXIII.) 



Oxytricha pellionella is one of the common species of the family 

 found in both stagnant infusions and fresh water. The flexibility 

 of the body is remarkable as it twists in and out among aquatic 

 plants. In the open its movement is a short jerky motion peculiar 

 to this and other species of the family. 



Reproduction by transverse division. Distribution general. 



Oxytricha platystoma Ehr. 



Body elongate-oval, posterior extremity slightly narrower than 

 the anterior. Usually five frontal, three to five scattered ventral 

 setae and five anal styles, none of which project beyond the poster- 

 ior border. Marginal setae forming a complete series. Peristome 

 area deep, extending about one-third the length of the body, the 

 anterior extremity of the right-hand margin conspicuously curved 

 to the left in a spiral manner. Nuclei two in number. Contractile 

 vesicle on the left side, anterior to the middle of the body. 

 Length, 150 microns. (Fig. 168, PI. XXIII.) 

 This species may readily be distinguished by the spiral nature 

 of the right-hand margin of the peristome area, which can be dis- 

 tinctly seen even from a dorsal view point. The species is not com- 

 mon in this state. Habitat, fresh water, with other species of the 

 genus, which it resembles in movement, manner of reproduction, 

 etc. 



HISTRIO Sterki. 



Somewhat elliptical in shape, inflexible. Frontal stj'les from 

 five to eight, ventral five, anal five. Marginal setae forming a 

 complete fringe. Peristome extending to, or nearly to, the middle 



