490 ORDER HOLOTRICHA. 



Placus striatus, Cohn. PL. XXVI. FIGS. 39 AND 40. 



Body ovate, slightly flattened, about twice as long as broad, the two 

 extremities rounded ; oral aperture circular, situated on the ventral surface 

 at a short distance from the anterior extremity ; cuticular surface furrowed 

 obliquely in opposite directions, and so producing a reticulate aspect. 

 Endoplast spherical, central ; contractile vesicle posteriorly situated. Move- 

 ments swift, in a straight line, rolling or rotatory on its long axis. Length 

 1-780". HAB. Salt water, among Conferva. 



Excepting for the absence of the vibratory oral membrane, Cohn* regards this 

 form as most nearly resembling Glaucoma ; the indurated and reticulate cuticle at 

 the same time corresponds to some extent with that of Coleps. 



GENUS IV. CONCHOPHTHIRUS, Stein. 



Animalcules free-swimming, persistent in shape, ovate or suborbicular, 

 with a convex dorsal and flattened ventral surface ; oral aperture situated 

 within a more or less funnel-shaped fossa or depression on the ventral 

 surface, followed by a tubular, recurved pharynx ; cuticular surface indurated, 

 delicately striate and ciliate throughout ; cilia fine, thickly set, usually 

 presenting a tufted or matted aspect ; endoplast and contractile vesicle 

 conspicuous. Occurring within the body-mucilage of various Lamelli- 

 branchiate and Gasteropodous Mollusca. 



Conchophthirus anodontae, Ehr. sp. PL. XXVI. FIG. 33. 



Body elongate-oval, depressed, about twice as long as broad, bluntly 

 rounded at the two extremities ; oral fossa spacious, occupying the centre 

 of the ventral surface, the pharyngeal tract recurved, extending to within 

 a short distance of the posterior extremity ; contractile vesicle simply 

 spherical, subcentral ; endoplast globular, posteriorly located. Length of 

 body 1-200". 



HAB. The body mucilage of Anodontidae and other fresh-water 

 Mollusca. 



This animalcule, selected by Stein as the type of the genus Conchophthirus, is 

 identical with the Leucophrys anodontce of Ehrenberg, and apparently also the 

 Plagiotoma acuminata of Claparede and Lachmann. The illustration here given of 

 this species is reproduced from T. W. Engelmann's "Zur Naturgeschichte der 

 Infusionsthiere," contained in the ' Zeitschrift fur Wissenschaftliche Zoologie ' for the 

 year 1861, where it is figured by way of comparison with Conchophthirus cttrtus, 

 described later on. 



Conchophthirus Steenstrupii, Stein. PL. XXVI. FIGS. 34 AND 35. 



Body broadly oval, depressed, equally rounded at the two extremities, 

 about one and a half times as long as broad ; oral fossa widely infundibular, 

 somewhat rectilinear, occupying the first third or quarter of the right-hand 



* " Neue Infusorien im Seeaquarium," ' Zeitschrift fur Wissenschaftliche Zoologie,' Bd. xvi., 

 1866. 



