580 ORDER HETEROTRICHA. 



is referred to in this volume as the ventral one upon which the oral aperture 

 debouches. Stein, on the contrary, in his figures and descriptions of these animal- 

 cules, distinguishes by such title the region lying to the right-hand of this aperture. 



Nyctotherus cordiformis, Stein. Pl. XXIX. Fig. 4. 



Body bean- or kidney-shaped in profile, somewhat pointed anteriorly, 

 much compressed, the breadth equal to two-thirds or three-quarters of the 

 total length ; pharyngeal cleft considerably surpassing in length the preced- 

 ing peristome-border, produced inwards to the centre of the body and then 

 recurved towards the ventral aspect ; the widened entrance or vestibulum 

 to the pharynx bearing on its lower edge a single long, stiff seta; striae 

 of the cuticular surface forming two convergent parallel systems, which meet 

 one another anteriorly, those forming the dorsal series occupying the larger 

 area ; endoplast elongate-oval, with a minute centrally attached endo- 

 plastule ; contractile vesicle single, postero-terminal. Length of body 

 1-168" to 1-108". 



Hab. — Parasitic within the intestinal viscera of frogs and toads. 



Nyctotherus ovalis, Leidy. 



Body broadly egg-shaped or shortly pyriform, often scarcely longer than 

 broad, the anterior extremity rounded ; pharyngeal cleft scarcely as long 

 as the peristome border, produced obliquely inwards to the centre of the 

 body, bearing no supplementary vestibular bristle ; cuticular strise forming 

 a single series, disposed in the same straight line from the apical to the 

 posterior extremity ; the anterior half of the body usually containing a 

 well-defined granular interspace ; endoplast elongate-oval, curved ; no 

 distinct endoplastule ; contractile vesicle single, subterminal. Length of 

 body 1-384" to 1-72". 



Hab. — Within the intestine of orthopterous insects, including various 

 species of Blatta and Gryllotdlpa. 



This species is identical with the Plagiotoma blattanim of Clapar^de and 

 Lachmann, and also of Stein in his earlier works. 



Nyctotherus gyoeryanus, Stein. Pl. XXXII. Figs. 20 and 21. 



Body oval or obovate, truncate or slightly kidney-shaped as seen in, 

 profile, moderately compressed ; pharynx equal in length to the peristome, 

 directed abruptly and obliquely inwards, having no supplementary vestibular 

 bristle ; cuticular striae or fibrillae of the sinistral region forming two 

 obliquely convergent, distinct fasciae, those of the dextral and ventral 

 surface forming a single oblique parallel series ; a clearly defined, granular, 

 kernel-like interspace enclosed at the anterior extremity; endoplast 

 elongate-fusiform ; contractile vesicle single, postero-terminal. Length 

 1-288" to 1-108". 



Hab. — The intestinal canal of Hydrophiliis pisceus, and other water 

 beetles. 



