EDMONDSON — PROTOZOA OF IOWA. lOI 



of the body. Nuclei two in number, contractile vesicle single, on 

 the left-hand side, near the middle. 



HiSTRIO STEINII Miill. 



Body elliptical, more than two times as long as broad, wider cen- 

 trally, evenly rounded at the ends. Three prominent frontal styles 

 with three or four additional smaller ones. Ventral styles scat- 

 tered. None of the five anal styles projecting beyond the posterior 

 border. Nuclei two, oval in form, one anterior to the mouth. 

 Length, i6o microns. (Fig. i66, PI. XXIII.) 

 Found frequently in fresh water, and also in infusions of pond 

 water, in many localities of the state. Reproduction is by trans- 

 verse division. 



STYLONYCHIA Ehrenberg. 



Elongate-oval in shape, inflexible. Eight frontal, five ventral 

 and five anal styles. Three long, hair-like setae, usually developed 

 from the posterior border. Peristome triangular, with a broad 

 base and sometimes with an undulating membrane. 



Stvlonychia mytilus Ehr. 



Bod}' elongate-oval, wider anteriorly, tapering toward a narrow 

 posterior extremity. Two right-hand anal styles, large and stout, 

 extending beyond the posterior margin. The hair-like caudal 

 setae very long and flexible. Peristome wide, extending nearly 

 to the middle of the body, the inner border with an undulating 

 membrane. Nuclei two, one anterior to the mouth. Contractile 

 vesicle single, near the left lateral border, posterior to the peris- 

 tome. 



Length, 200-400 microns. (Fig. 169, PI. XXIII.) 



StvJonvchia mytilus is one of the largest .species of the family 

 occurring in the waters of this state. The posterior extremity of 

 the body is often variable in shape and character, sometimes being 

 pointed and curved, .sometimes truncated, but nearly always 

 sharpl}' contrasted, by its tran.sparency, with the remaining more 

 granular portion of the body. 



Frequently the anal styles and caudal setae present a branched 

 appearance. Reproduction is by transverse division. Distribu- 

 tion is general. Found in infusions of pond water. 



