630 ORDER PERITRICHA. 



Fam. III. ACTINOBOLID-ffi, S. K. 



Animalcules free-swimming, ovate or globose ; oral aperture terminal, 

 surrounded by a fringe of adoral cilia, supplemented by numerous retractile 

 tentaculiform appendages. 



Although the tentaculiform appendages in the as yet single known animalcule 

 referred to this family are described by Stein as resembling those of the Acinetida 

 between which and the Ciliata he regards it as an annectant type it seems hardly 

 probable that such structures actually exist in company with a well-developed oral 

 aperture. It would seem more likely, on the other hand, that they find their homo- 

 logues in the retractile setae of Stentor, or in the springing-hairs of Halteria and 

 Mesodinium. To the family group embracing the two last-named generic forms 

 it is not improbable, indeed, that Actinobolus may have hereafter to be transferred. 



GENUS I. ACTINOBOLUS, Stein. 



Animalcules free-swimming, ovate or globular ; oral aperture perforating 

 the centre of the apical extremity, encircled by short even-sized cilia, among 

 which are scattered numerous thread-like tentacula capable of extension 

 or retraction within the substance of the parenchyma, like those of the 

 Acinetidae ; anal aperture postero-terminal ; endoplast and contractile 

 vesicle conspicuous. 



Actinobolus radians, Stein. 



Body irregularly ovate or subglobose, the anterior extremity produced 

 as a short nipple-shaped or snout-like projection pierced by the oral aper- 

 ture and bearing the oral cilia and retractile tentacula ; endoplast elongate, 

 cord-like, irregularly curved ; contractile vesicle large, spherical, postero- 

 terminal. Dimensions unrecorded. 



HAB. Fresh water, among Lemnce. 



It is to be regretted that Stein has not published a more exhaustive account, 

 with an illustration, of this remarkable animalcule ; the only description at present 

 available for reference being a few lines in a footnote, p. 169 of the second volume 

 of his ' Organismus.' Although placed by him among the Holotricha, it is not stated 

 that the cuticular surface bears cilia throughout, those 'around the oral aperture 

 alone being mentioned. 



Fam. IV. HALTERIID^E, Clap. & Lach. 



Animalcules free-swimming, persistent in shape, more or less globose 

 or ovate, bearing a spiral or subcircular wreath of adoral or locomotive 

 cilia, these occasionally supplemented by a girdle of long hair -like 

 springing-setae ; oral aperture terminal, central or eccentric ; trichocysts 

 sometimes developed. 



The several genera here united under the family title of the Halteriidae, while 

 harmonizing tolerably with one another in general contour and comportment, present 

 among themselves so considerable a variation in the composition of their oral and 

 ciliary systems, that their separation into more numerous, but less comprehensive, 

 groups of equivalent value, was at first determined. A closer study of them, how- 



