nevj Infusoria from American Fresh Waters. 99 



by four compressed, equidistant, somewhat obliquely directed 

 keel-like elevations, thus exhibiting in horizontal optic section 

 four diverging wing-like appendages or processes ; oral aper- 

 ture conspicuous ; flagellum about twice as long as the body ; 

 endoplasm transparent, colourless. Length of body yyVs ii^ch. 



Hah. Pond-water, with Ceratophyllura fhrnersurn^ L. 



In fig. 2 is delineated a diagrammatic horizontal optic 

 section, showiiig the arrangement of the alse. 



Clostenema*, gen. nov. 



Animalcules naked, free-swimraing, fusiform or elongate, 

 persistent in sliape ; flagella two, diverse in length, originating 

 near together at the anterior border, the longer extended in 

 advance, the shorter usually held beneath the lower surface, 

 both vibratile ; pharyngeal passage present, and apparently 

 communicating with the contractile vesicle. 



Clostenema sociolis, sp. nov. (PI. I. fig. 3.) 



Body fusiform, three times as long as broad, the frontal 

 border obliquely emarginate, the posterior extended in a short 

 rounded prolongation ; long flagellum equalling or exceeding 

 the body in length, the short one about one fourth or one fifth 

 the length of the infusorian ; pharyngeal passage extremely 

 narrow ; contractile vesicle double, in the anterior body-half, 

 near one lateral border ; nucleus apparently subcentral ; endo- 

 plasm colourless, slightly granular. Length of body y^Qo inch. 

 Anal aperture not observed. 



Hah. Standing water, with Lemna. Gregarious. 



Reproduction takes place by longitudinal fission, presu- 

 mably after conjugation, which was observed. While swim- 

 ming the animalcules advance evenly and rather slowly without 

 revolution on their axis, the long flagellum being held in 

 advance, the distal extremity most actively vibrating. The 

 favourite position seems to be a quiescent one in companies, 

 with the frontal border in contact with a mass of debris, or an 

 algal filament, the flagella vibrating and extending quickly in 

 various directions. No oral aperture could be positively dis- 

 cerned, although what 1 have interpreted as a very naiTOW 

 phaiyngeal passage was apparent. The granules within the 

 endoplasm have a tendency to collect in the posterior prolon- 

 gation, as if an anal aperture might be present there, but none 

 has yet been noticed. The entrance of solid food-particles 

 through the pharynx also escaped prolonged observation. 

 Its systematic position is probably among the Spheno- 



* (cXojo-rijr, a spindle ; i^/ia, a thread. 



