106 Dr. A. C. Stokes on some 



sion, but are there met by the cilia of the right-hand margin, 

 which do not conspicuously differ from those clothing the 

 cuticular surface. From the remaining families of the order 

 this Infusorian is excluded by the linear arrangement of cilia 

 just referred to ; the formation of a new family group will there- 

 fore be necessary for its reception, the position of the new 

 group in a system of classification being immediately following 

 Stein's Bursariadgs and preceding the Spirostomid^ of Kent, 

 Histiobalantiidffi necessarily being the family title. 



Histiohalantium agile, sp. nov. 

 (PL I. figs. 15 and 16.) 



Body ovate, one and a half times as long as broad, some- 

 what depressed, the dorsal surface convex, the ventral slightly 

 flattened, both extremities evenly rounded ; the left-hand 

 body-margin evenly convex, the right-hand border gibbous ; 

 cuticular cilia abundant, curved ; numerous long, fine, setose 

 hairs projecting from all parts of the surface ; oral fossa ovate, 

 capacious, situated near the centre of the right-hand side of 

 the ventral aspect, its posterior region supporting a conspicuous 

 retractile and freely motile infundibuliform membranous sack, 

 which is posteriorly prolonged as a narrow, flexible, mem- 

 branous, and tubular passage leading to the oral aperture, and 

 anteriorly continued as a broad undulating membrane attached 

 to the right-hand border of the oral fo?sa, and as an incon- 

 spicuous membranous velum adherent to the left-hand side of 

 the same depression and enclosed within it ; adoral cilia on 

 the left-hand margin of the oral depression long, fine, setose ; 

 a broad tuft of long setose cilia springing from the frontal 

 border of the oral fossa and directed backward, a second broad 

 tuft of vibratile setose cilia anteriorly enclosed within the oral 

 cavity, attached to the anterior superior wall, their posterior 

 extremities free ; oral aperture near the posterior extremity of 

 the body, followed by a short somewhat adcurved pharyngeal 

 passage ; contractile vesicles small, multiple, scattered ; 

 nucleus ovate, situated near the anterior border ; anal aper- 

 ture not observed ; endoplasm granular, colourless, transparent. 

 Length of body ayj inch. 



Hah. Fresh water, wit»h Ceratophyllum. 

 The enclosed adoral sack and its posterior tubular prolon- 

 gation appear to be adherent to the walls of the oral fossa 

 only at the points where the tubular passage surrounds the 

 oral aperture, and anteriorly by the membranous continuation 

 of the infundibulum. The entire organ, composed of bag-like 

 velum and tubular adoral passage, is freely motile, being 

 vaiiously protruded and retracted and rolled from side to side, 



