new Infusoria from American Fresh Waters. 105 



of the oval aperture elongates, an opening, which finally be- 

 comes the mouth of the anterior moiety, forming at or near 

 the frontal border and developing from each side a very con- 

 spicuous vibratile membrane, the one on the right-hand margin 

 usually being the larger. The frontal cilia are then also 

 more conspicuous and apparently larger than in the mature 

 individual. The dividing portion finally separates, having the 

 posterior tail-like prolongation and a terminal oral aperture 

 containing the two prominent membranes, leaving the posterior 

 or original animalcule apparently unchanged. The separated 

 moiety, which at first but remotely resembles the mature animal- 

 cule, remains sluggish for some time. The large, projecting, 

 flap-like membranes on the frontal border seem to be an in- 

 cumbrance, and, until the oral aperture assumes its proper 

 position and the membranes become enclosed, the Infusorian 

 seldom moves unless jostled by some more active inhabitant 

 of the live-slide, when it quickly darts forward only to resume 

 its quiet waiting. The existence of the two vibratile flaps 

 might readily have been overlooked, or the two mistaken for 

 a single one, if reproductive fission had not been observed, 

 since to sepai-ate them, even with a high-power objective, is 

 no easy matter. 



HiSTiOBALANTiUM*, gen. nov. 



Animalcules free-swimming, heterotrichous, ovate, some- 

 what depressed, persistent in shape, the ventral aspect flat- 

 tened ; setose hairs abundantly developed on all parts of the 

 surface ; the oral fossa near the centre of the ventral aspect, 

 on the left-hand side of the median line, ovate, capacious, the 

 cilia of the left-hand border long, fine, setose, the frontal wall 

 bearing a ciliary tuft, and the right-hand margin supporting 

 an undulating membrane, which forms posteriorly a freely 

 motile infundibuliform sack continued backward as a narrow 

 membranous tubular passage, at the posterior extremity of 

 which is the oral aperture, the oral fossa also enclosing ante- 

 riorly a secondary vibratile tuft of long cilia ; contractile 

 vesicle multiple ; nucleus ovate, anteriorly situated. 



Inhabiting fresh waters. 



This Infusorian is excluded from the Bursariada3 of Stein 

 by the presence of the vibratile membrane, to say nothing of 

 the remarkable infundibuliform sack with the tubular poste- 

 rior prolongation and the anterior ciliary tufts. Tlie adoral 

 cilia fringing the left-hand border of the oral fossa apparently 

 do not surround the posterior margin of the peristomial depres- 



* lo-Tioi/, a meuiLraiie ; iiiiKavtiov, a little saclf. 

 Ann. cfc Mag. N. Hist. Ser. 5. Vol. xvii. 8 



