No. 2.] FRESH-WATER PROTOZOA. 5 1 



like peristome, from which protrudes a large undulating 

 membrane. Cilia long ; striation regular ; nucleus spher- 

 ical, and contractile vacuole terminal. Trichocysts some- 

 times present. 

 Cyclidium Ehrbg. 



Very similar to Pleuronema and frequently united with 

 it. Differs in being smaller, having a shorter peristome 

 and one or more long bristles at posterior end. 



Figs. 208 a, b, and c, represent three types of Cyclid- 

 ium, perhaps Cy. glaucoma. Fig. 209 is Stokes' species, 

 Cy. limetosum. Figs. 211 to 215 are undetermined spe- 

 cies, apparently referable to the genus Pleuronema. 

 Mesodinium Stein. 



Small, pear-shaped, with a furrow in the middle; an- 

 terior end conical ; the mouth at anterior end leads into a 

 long pharynx. Posterior end spherical. In the furrow 

 is a crown of strong cilia, which is occasionally wanting. 

 Four small knob tentacles around the mouth. Nucleus 

 spherical to kidney-shaped, central. Anus and contrac- 

 tile vacuole terminal. 

 M. sp. (?), Fig. 135. In this specimen the knobs were not 

 seen. 

 Urocentrum Nitzsch. 



Somewhat cylindrical, with a constriction sHghtly be- 

 hind the middle. Mouth posterior, surrounded by a flat- 

 tened area, with a furrow extending backwards ; a row of 

 closely arranged cilia, extending as a girdle around the 

 body. A short pharynx. The anterior part of the body 

 uniformly ciliated, with a broad zone of cilia near the mid- 

 dle and posterior end. A prominent tuft of fused cilia at 

 posterior extremity. Nucleus worm-shaped, in the hinder 

 part of the body, with round, secondary nuclei. Anus and 

 contractile vacuole terminal. 

 Ur. turbo Miill., Fig. 210. 

 Lionotus Wrz. 



Elongated, with a flattened, ciliated, ventral (right 

 side) surface, and a convex, dorsal (left side) surface; 

 commonly with an evident proboscis, which is hyaline, as 

 is also the short caudal extremity. On the left side of pro- 



