GENUS PETALOMONAS. 371 



and not incepted food-substance, they are referable probably to the family groups 

 of the Euglenidae or Chrysomonadidae. The present type was originally included 

 by De Froraentel in the genus Monas. 



Paramonas deses, Ehr. sp. 



Body oblong, rounded at the two extremities, colour bright green, 

 ora^aperture distinct, situated at the base^of the flagellum, the latter organ 

 long and undulating; contractile vesicle central. Length 1-1200". 



HAB. Fresh water ; solitary. 



Identical with the Monas deses of Ehrenberg and De Fromentel. 



GENUS II, PETALOMONAS, Stein. 



Animalcules free-swimming, ovate, depressed, with a single long vibratile 

 flagellum ; cuticular surface indurated, often carinate ; oral aperture distinct, 

 situated close to the base of the flagellum. 



Stein first founded this genus upon the Cyclidium absdssum of Dujardin, to which, 

 in his recently published work,* several distinct forms are added. Dujardin's 

 generic title of Cyclidium having been previously employed by Ehrenberg for certain 

 ciliate animalcules, cannot be retained among the Flagellata. 



Petalomonas abscissa, Duj. sp. PL. XX. FIGS. 5 AND 6. 



Body subtriangular or irregularly ovate, flattened and leaf-like, slightly 

 pointed anteriorly, the posterior margin somewhat truncate, the dorsal 

 surface traversed longitudinally with one or occasionally two keel-like 

 elevations ; parenchyma transparent, slightly granular ; flagellum slender 

 throughout, about twice the length of the body, directed rigidly in advance, 

 and vibrating only at its anterior extremity ; movements slow and even ; 

 multiplying by longitudinal subdivision. Length 1-900". 



HAB. River water. 



While the subtriangular outline indicated in the accompanying figures represents 

 the more typical contour of this species, Stein's illustrations show that examples 

 occur in which the posterior border is evenly rounded as in P. mediocanellata, while 

 more rarely the lateral borders may be irregularly contorted, or two keel-like 

 elevations are developed on the dorsal surface. 



Petalomonas mediocanellata, Stein. PL. XX. FIG. 3. 



Body flattened, resembling an apple-pip in shape, acuminately pointed 

 anteriorly, rounded and widest posteriorly, about twice as long as broad, a 

 straight narrow groove or channel extending down the median line of the 

 ventral surface from the oral aperture nearly to the posterior border; 

 flagellum equalling or slightly exceeding the length of the body; contractile 

 vesicle situated towards the anterior extremity at the left-hand side of the 

 median groove, the endoplast located further back on the opposite side of 

 this same channel. Length 1-700". HAB. Fresh water. 



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



2 B 2 



