372 ORDER FLAG ELLA TA-E US TOMATA. 



Petalomonas sinuata, Stein. PL. XX. FIG. 4. 



Body flattened, obtusely pointed anteriorly ; the posterior margin widest, 

 singly or doubly emarginate, its two lateral angles prolonged outwards, no 

 median ridge or channel, but a short oblique groove produced from the 

 oral aperture towards the right-hand border ; flagellum nearly equalling 

 twice the length of the body ; endoplast and contractile vesicle as in 

 P. mediocanellata. Length 1-800". 



HAB. Fresh water, dividing by longitudinal fission. 



Petalomonas ervilia, Stein. PL. XX. FIG. 7. 



Body flattened, elongate, ovate or elliptical, slightly pointed anteriorly, 

 twice as long as broad ; the ventral surface with a broad groove or channel 

 that extends along the left lateral border from the anterior to the posterior 

 extremity ; flagellum exceeding the length of the body ; contractile vesicle 

 and endoplast situated as in the preceding species, the former sometimes 

 presenting a compound aspect. Length 1-580". HAB. Fresh water. 



Doubtful species. 



The Cyclldium nodulosum and crassum of Dujardin are probably referable to 

 the genus Petalomonas, but the presence of an oral aperture in these forms has yet 

 to be demonstrated. Their brief diagnostic characters, as given by Dujardin, are 

 herewith appended. 



Cyclidium (Petalomonas?} nodulosum, Duj. Body flat, discoidal, nodular 

 and vacuolate, movements slow. Length 1-500". 



HAB. River water, with Myriophyllum. 



Cyclidium (Petalomonas ?) crassum, Duj. Body thick and rounded at the 

 edges; flagellum thickest at the base, slightly undulating; movements 

 active and in a zigzag direction. Length 1-1700". HAB. Ditch water. 



A small animalcule, as represented at PI. XX. Figs. 8 and 9, has been recently 

 obtained by the author from hay infusions, whose position would appear to be 

 among or closely adjacent to the representatives of the genus Petalomonas. Their 

 contour, while persistent, is less flattened than that of the more normal species 

 previously described, and was observed to vary considerably in different individual 

 zooids. In most instances, as at Fig. 8, the animalcules were symmetrically ovate, 

 as in P. abscissum, but somewhat more elongate and less flattened, without any 

 groove or keel-like ridge, while more rarely they were altogether irregular and 

 nodulate, as shown at Fig. 9. The average length of these animalcules did not 

 exceed 1-2500". 



The mode of progress through the water normally exhibited by this type is 

 peculiar, and may assist perhaps in the substantiation or otherwise of its claim for 

 admission to the generic group wherein it is here relegated, though unfortunately 

 no data have as yet been published concerning the characteristic comportment of 

 the several species already enumerated. Such locomotion in the present instance 

 was always accomplished steadily forwards and in a straight line, the body and 

 terminal flagellum being depressed at the angle indicated in the accompanying 

 illustrations; the distal end only of this last-named appendage was maintained 

 in a state of vibration, and was thrust here and there over the surface of the 

 slide or surrounding debris, apparently in search of food. Not unfrequently the 



