Stokes.] 22 [j un e 19, 



a fact worthy of note that the greater proportion of the Infusoria thus far 

 there obtained belong to one family, the Oxytrichidae of Ehrenberg. 



With the exception of certain forms mentioned in this paper, there are 

 but four genera included in the Oxytrichidae without that posterior cluster 

 of appendages named from their position the anal styles. Their presence 

 or absence is therefore of diagnostic value. It is their absence that sep- 

 arates Hemicycliostyla from Urostyla, which it otherwise closely resembles, 

 even in form and movements. Its position in the family group is evidently 

 lower than that of Urostyla, simply because these posterior ventral appen- 

 dages have not been developed, 



Hemicycliostyla (jj/j-ckukXco^^ semicircular; aruluq^ a style), gen. nov. 

 Animalcules free-swimming, more or less elongate-ovate, soft, flexible and 

 elastic, the extremities rounded ; frontal styles twenty or more, arranged 

 in two more or less semicircular rows ; adoral ciliary fringe beginning near 

 the center of the right-hand side of the peristome-field ; ventral surface 

 entirely clothed with fine setae arranged in closely approximated longitu- 

 dinal rows ; anal styles absent ; contractile vesicle single or double ; 

 nucleus multiple. 



Hemicycliostyla sphagni, sp. nov. (Figl). Body elongate-ovate, soft, flex- 

 ible and extensile, four times as long as broad, widest behind the center ; 

 tapering to the rounded posterior extremity and to the convex, narrower 

 frontal extremity which is curved toward the left-hand side ; frontal styles 

 about twenty, in two semicircular rows ; marginal setae not differing from 

 the ventral, scarcely projecting beyond the body-margin except at the 

 posterior border ; peristome-field confined to the anterior third of the ven- 

 tral surface, the right-hand margin ciliate and bearing a membrane ; ado- 

 ral cilia short ; nucleus multiple, the nodules ovate or subspherical, small, 

 numerous and scattered ; contractile vesicle double, spherical, placed near 

 the left-hand side of the anterior body-half ; anal aperture dorsal, near the 

 posterior extremity ; parenchyma vacuolar ; hispid dorsal setae small. 

 Length of body 1-50 to 1-60 inch. Habitat. — Marsh water, with Sphag- 

 num. 



There is another form (Fig. 2) resembling this in a general way, but 

 readily distinguishable from it, not only in shape and size, but chiefly by 

 the presence of a single contractile vesicle, the greater abundance of the 

 nuclear nodules, the absence of vacuolar spaces within the endoplasm, 

 and the development of a conspicuous series of par-oral cilia on the inner 

 edge of the left-hand border of the peristome-field. The body is also less 

 extensile than in H. sphagni, and the Infusorian is somewhat less active in 

 its movements. In both the endoplasm is usually made dark and almost 

 opaque by the great quantity of granular matter crowding it centrally. 



Hemicycliostlya trichota, sp. nov. (Fig. 2). Body elongate-ovate, some- 

 what extensile, about three times as long as broad, widest posteriorly, ta- 

 pering to the anterior extremity, which is slightly curved toward the left- 

 hand side ; frontal styles and ventral setae essentially as in H. sphagni; 

 peristome-field confined to the anterior half of the ventral surface, a series 



