GENUS A TRA C TONE MA . 373 



animalcules effect a momentary adherence by the distal region of this flagellum, and 

 swinging their bodies round upon it as though on a pivot, direct their course in an 

 opposite direction. It is provisionally proposed to distinguish this species by the 

 name of Petalomonas irregularis. The presence of a distinct oral aperture has not 

 as yet been definitely certified. 



GENUS III. ATRACTONEMA, Stein. 



Animalcules free-swimming, persistent in shape, fusiform or elongate ; 

 flagellum single, terminal ; oral aperture at the base of the flagellum, 

 followed by a distinct tubular pharynx, the posterior termination of which 

 apparently communicates freely with the contractile vesicle ; endoplast 

 subcentral ; endoplasm transparent, finely granular. Inhabiting fresh water. 



Atractonema teres, Stein. PL. XX. FIGS. 10-12. 



Body elongate fusiform, widest centrally, attenuately pointed at each 

 extremity, four or five times as long as broad ; flagellum slender, vibratile, 

 equalling the body in length ; posterior termination of the pharynx, and 

 communicating contractile vesicle almost joining the central spheroidal endo- 

 plast ; endoplasm finely granular, often enclosing between the endoplast 

 and posterior termination a discoidal amylaceous corpuscle. Length 1-640". 



HAB. Fresh water, dividing by longitudinal fission ; movements, repent 

 and rotatory. 



In accordance with the index to Stein's figures,* the representatives of this 

 species swim freely through the water or creep, head downwards, with the attenuate 

 oral region applied to the surface of the objects traversed. In some of the examples 

 delineated, see PI. XX. Fig. 12, the flagellum has disappeared, and the central 

 endoplast become enlarged and broken up into spore-like bodies. 



GENUS IV. PHIALONEMA, Stein. 



Animalcules free-swimming, persistent in form, more or less flask-shaped ; 

 oral aperture terminal, dilated, bearing on one side a single flagellum, 

 succeeded by a curved tubular pharyngeal dilatation, which is produced 

 backwards to or beyond the centre of the body; endoplasm transparent 

 granular ; contractile vesicle and endoplast distinct. Inhabiting fresh 

 water. 



Phialonema cyclostomum, Stein. PL. XX. FIGS. 13 AND 14. 



Body flask-shaped, somewhat gibbous, about three times as long as 

 broad, widest centrally, pointed posteriorly, with a neck-like anterior pro- 

 longation, the extremity of which is obliquely truncate, and forms a circular, 

 thick-bordered, expanded rim around the oral excavation ; curved tubular 

 pharynx, often produced backwards to within a short distance of the 

 posterior extremity, its distal end much dilated ; cuticular surface usually 

 obliquely striate, but these striae occasionally replaced by a few spirally 

 disposed projecting ribs ; flagellum short, vibratile, nearly equalling the body 



* ' Infusionsthiere,' Abth. iii., 1878. 



