GENUS KERONA. 763 



angular, its reflected border ciliate ; setae of the median ventral rows few in 



number, including about five or six in the right and three in the left-hand 



row, long, slender, and widely separated ; marginal setae few, distant, and 



similar in character to those of the ventral series ; contractile vesicle 



developed close to the centre of the left lateral border, exhibiting at 



systole short canal-like prolongations ; endoplasts double, median, one 



situated in advance of and the other posterior to the terminal border of 



the peristome. Length I-300" to 1-240". 



Hab. — Fresh water. 



The scattered and irregular disposition of the ventral and marginal setas, 

 together with their attenuate form, lend to this species an untidy aspect that serves 

 to distinguish it readily from all other members of the H)-potrichous group. The 

 irregular development of the stylate appendages is found to extend itself to the large 

 adoral cirri, which are also comparatively few in number and widely separated. 



Genus II. KERONA, Ehrenberg. 



Animalcules free-swimming, persistent in shape, flattened or plano- 

 convex, subreniform ; possessing no true frontal, ventral, or anal styles, 

 but in place of these several arcuate rows of short ventral setae ; a row of 

 similar but longer marginal setae forming a continuous fringe around the 

 peripheral border; endoplast usually double; contractile vesicle single, 

 spherical, situated near the posterior border of the peristome. Inhabiting 

 fresh water. 



Kerona polyporum, Ehr. Pl. XLIII. Figs. 4 and 5. 



Body kidney-shaped, plano-convex, the anterior end evenly rounded, 

 the posterior extremity slightly pointed, the right border convex, the left 

 one deeply indented centrally ; setae of the ventral surface disposed in six 

 subparallel rows, three of which originating close to the right-hand margin 

 of the peristome, extend obliquely nearly to the left-hand border of the 

 posterior half of the body, the other three shorter rows confined to the 

 anterior body-half; the five hindermost setae of the most posterior row 

 larger than any of the preceding and apparently representing the five anal 

 styles of the more normal Oxytrichidae ; peristome-field extending back- 

 wards nearly to the centre of the body, its inner border ciliate, reflected at 

 an acute angle, and almost parallel with the outer one ; cilia of the external 

 or left-hand peristome-border very long and fine, forming with the marginal 

 setae an almost uninterrupted fringe around the animalcule's body. Length 

 i-190" to 1-120". 



Hab. — Fresh water, occurring as an ectoparasite or commensal on 

 various species of Hydra. 



This animalcule is among the first discovered infusorial forms, it having attracted 

 attention through its frequent occurrence — in company with Trichodina pediculus — 

 upon the surface of the fresh-water polypes Hydra fusca and H. vulgaris. By many 

 earlier writers the distinctions between Kerona and Siylonychia have been very 

 insufficiently defined, but in accordance with the diagnosis of the present genus as 



