EDMONDSON — PROTOZOA OF IOWA. 9 1 



be assumed by the same individual; sometimes the posterior 

 region is flattened and at times the anterior extremity lacks the 

 obliquely twisted appearance. A form, which probably is a phase 

 of this species, has been observed in Johnson county, with a greatly 

 inflated posterior region and an acute anterior twisted extremity. 

 In the anterior extremity of the normal specimen the endoplasm 

 usually encloses a mass of dark pigment-like granules. The 

 motion of the organism is accompanied by a slow revolution on 

 its longitudinal axis. 



METOPIDES Quennerstedt. 



Ovate or pear-shaped, usually broader anteriorly. The anterior 

 region folded obliquely across the ventral surface. Oral furrow 

 produced by the folded portion. Oral aperture at the posterior 

 tip of the furrow. Cilia of oral groove large, a tuft of long setae 

 produced from the posterior border, 



Metopides acuminata Stokes. 



Body pear-shaped, broadh' rounded anteriorly, tapering toward 

 a posterior, tail-like prolongation from which extend a number of 

 long, slender setae. Nucleus spherical, centrally located. Con- 

 tractile vesicle in the posterior region. 



Length, 75 microns. (Fig. 147, PI. XX.) 



This species differs from Metopiis sigmoides principally in the 

 contour of the body and the presence of the posterior tuft of long 

 setae. Endoplasm is usually transparent and the nucleus visible 

 without the aid of reagents. Found in stagnant water but not 

 abundant. In motion, rapidly rotating on the longitudinal axis. 



SPIROSTOMUM Ehrenberg. 



Greatly elongated but highly contractile, cylindrical, anterior 

 border rounded, posterior border often truncate. Oral furrow 

 extending from the anterior extremity backward to the middle of 

 the body, the left-hand border strongly ciliate. Pharynx short. 

 Body contracting spirally. , 



Spirostomitm ambiguum Ehr. 



Body elongated, from ten to fifteen times as long as broad. 

 Oral aperture at the posterior end of the longitudinal oral furrow. 

 Nucleus moniliform, greatly elongated. Contractile vesicle 



