46 DAVENPORT ACADEMY OF SCIENCES. 



in one or more regions; both flagella vibratile, one equalling 

 the body in length, the other about one-half that length. Endo- 

 plasm transparent with dark colored corpuscles, which are shifted 

 about by the movements of the body. Nucleus central, contrac- 

 tile vesicle in the anterior region. 



Length of the extended body, 95 microns. 



Figure 74, Plate X, illustrates the species as it commonly 

 appears in a mature condition and extended. Fig. 75 represents 

 the partially contracted state. 



The species is not uncommon in pond water. 



Family, PERANEMID^. 



HETERONEMA Dujardin. 



Body oval or elongated, changeable in shape. Flagella two in 

 number, one directed forward, one trailing, both arising from the 

 anterior extremity. Oral aperture near the base of the flagella. 



Heteronema acus Ehr. 



Body greatly elongated when extended, wider centrally, taper- 

 ing toward each extremity. Anterior flagellum about as long as 

 the body and twice as long as the trailing one. Contractile vesi- 

 cle in the anterior extremity, nucleus centrally located. 

 IvCngth, when extended, 50 microns. (Fig. 76, PL X.) 

 Heteronema acus is exceedingly plastic and changeable in form, 

 becoming shortened and greatly distended on contraction. The 

 long anterior flagellum is not highly vibratile. P'ound in fresh 

 water in Johnson and Keokuk counties. 



PETALOMONAS Stein. 



Somewhat oval, flattened, and of hardened consistence. Fla- 

 gellum single. Oral aperture distinct. 



Petalomonas mediocanellata Stein. 



Body ovate, flattened, persistent in shape, broadly rounded 

 posteriorly, tapering to an acutely pointed anterior extremity. 

 Flagellum single, arising from the anterior extremity and directed 

 in advance of the body, a distinct groove leading from the base 

 of the flagellum posteriorly. 



Eength of J;he body, 30-40 microns. (Fig. 77, PI. XI.) 



