544 ORDER HOLOTR1CHA. 



Pleuronema coronata, S. K. PL. XXVII. FIG. 56. 



Body ovoid, compressed, twice as long as broad, extremities subequally 

 rounded, or slightly wider anteriorly ; oral fossa almost central ; cuticular 

 surface dotted with short, fine, rigid cilia or setae, whose length equal one- 

 sixth only of the diameter of the body ; a few supplementary, consider- 

 ably longer, fine, rigid setae projecting at various angles from the anterior 

 .extremity. Length of body 1-290". HAB. Freshwater. 



The author, not concurring with Claparede and Lachmann in referring the form 

 answering to the above diagnosis, and as figured by those authorities, to the Pleu- 

 ronema chrysalis of Ehrenberg, Dujardin, and Perty, a new specific title has been 

 created for its reception. The contour of its body is shorter and thicker than that of 

 P. chrysalis, from which it may also be readily distinguished by the short character 

 of the setae of the general cuticular surface and by the presence of supplementary 

 longer setae at the anterior extremity. The Pleuronema chrysalis, as figured by 

 Quennerstedt,* is apparently also identical with this type. 



GENUS II. CYCLIDIUM, Ehrenberg. 



Animalcules free-swimming, persistent in form, ovate, more or less com- 

 pressed ; oral aperture ventral, supplemented by a hood-shaped extensile 

 membrane ; body clothed with fine, rigid, hair-like setae, one or more abnor- 

 mally long caudal setae developed at the posterior extremity; contractile 

 vesicle single, posteriorly situated ; cortical layer not containing tricho- 

 cysts. Inhabiting salt and fresh water. 



This genus, originally instituted by Ehrenberg, corresponds with the Atyscum 

 and Enchelys, in pars, of Dujardin, both of which are now accepted as comprising 

 forms fundamentally identical with Cyclidium glaucoma. Claparede and Lachmann, 

 as well as Stein, have further proposed to incorporate with this genus the Uronema of 

 Dujardin a decision, however, from which the present author dissents, he having 

 frequently met with an animalcule which, while accurately corresponding with 

 Dujardin's Uronema marinum, differs essentially from Cyclidium as here defined, in 

 the character of the body cilia. The long caudal seta, and the situation of the 

 contractile vesicle, serve at the same time to distinguish the animalcules of this 

 genus from those of Pleuronema, which they otherwise closely resemble. The 

 several known species of Cyclidium are exceedingly minute, and require the employ- 

 ment of the higher magnifying powers of the compound microscope for the satis- 

 factory illustration of their characteristic membraneous trap. All the species are 

 very agile, springing about rapidly when disturbed by aid of the stiff setae with which 

 the general surface of their cuticle is beset, while at other times they progress 

 forwards leisurely by means of the vibratile cilia adjacent to the oral fossa. 



Cyclidium glaucoma, Ehr. PL. XXVII. FIGS. 57 AND 58. 



Body ovate, compressed, somewhat reniform, convex above, concave 

 beneath, little over twice as long as broad ; the oral aperture situated a 

 little in advance of the centre of the ventral surface ; setae of the general 

 surface very long and fine, their length equalling or exceeding that of the 

 breadth of the body, disposed in even longitudinal lines, the posterior or 

 caudal seta conspicuous, twice the length or more of those of the general 



* ' Sveriges Infusoriefauna,' Lunds Universitets Ars-skrift, Tab. I. fig. 19, 1871. 



