GENUS PLAGIOTOMA. 583 



Excepting for the presence of the posterior setse, the single representative of this 

 genus would appear to coincide entirely w\x\\.Nfetopus. Similar, though more numerous, 

 setffi are indeed, according to Stein, possessed by Metopus in the earher phases of its 

 growth. 



Metopides contorta, Quenn. Pl. XXXII. Fig. 18. 



Body elongate-ovate, about two and a half times as long as broad, 

 rounded posteriorly ; the anterior third folded obliquely to the left, across 

 the ventral aspect ; cuticular surface striate longitudinally, cilia long and fine, 

 matting together in a tuft-like manner; posterior sets two in number; 

 contractile vesicle postero-terminal. Length 1-275". Hab.— Salt water. 



Genus VI. PLAGIOTOMA, Dujardin. 



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

 lamellate, the ventral margin straight, the dorsal one convex ; oral aperture 

 situated on the ventral surface ; peristome-field extending from the 

 anterior extremity to the oral aperture, bearing a row of adoral cilia on the 

 left side only, continued inwards at the oral entrance so as to form an 

 obliquely directed tubular pharynx, a single long bristle protruding from 

 the lower border of the pharyngeal cleft ; anal aperture postero-terminal, 

 not conspicuous. Inhabiting the intestinal viscera of invertebrate animals. 



Plagiotoma lumbrici, Duj. Pl. XXIX. Fig. 10. 



Body ffem three to four times as long as broad, compressed, lanceolate 

 or almond-shaped, transparent, margin of the ventral surface straight, that 

 of the dorsal one convex, posterior termination usually obliquely truncate ; 

 oral aperture situated a little way behind the centre of the ventral surface ; 

 pharyngeal cleft curved, produced downwards and backwards nearly to the 

 central axis of the body ; endoplast ribbon-like, convolute or racemose ; 

 contractile vesicle single, located close below the pharyngeal cleft. Length 

 I-192" to 1-120". 



Hab. — Intestine of the common earthworm, Lmnbriais terrestris. 



This species is identical in part with the Faramecium compressiim of Ehrenberg, 

 and was first noticed by Gleichen in the year 1781 under the title of the Bean- 

 animalcule or " Bohnenthierc/ien." 



Fam. II. SPIROSTOMIDiE, S. K. 



Animalcules free - swimming, usually more or less flattened, rarely 

 cylindrical, often attenuate ; peristome-field excavate, extending along the 

 left side of the ventral surface from the anterior extremity towards the 

 centre of the body, the oral aperture located in the angle formed by the 

 posterior border of the peristome; larger adoral cilia forming a right- 

 winding or dextrotropous spire, continued along the entire outer margin of 

 the peristome-field, or confined to the posterior portion only of this area, 

 the inner border of the peristome occasionally bearing an undulating 

 membrane ; anal aperture posteriorly situated. 



