72 ORDER HYPOTRICHA. 



Uroleptus and Oxytricha, the form of the body according with the former, and the 

 character and disposition of the setae corresponding more closely with those of the 

 last-named genus. 



GENUS XV. STYLONETHES, Sterki. 



Animalcules free-swimming, widest and rounded posteriorly, narrowed 

 anteriorly, more or less thick or inflated ; the anterior half of the frontal 

 region bearing numerous, from fifteen to twenty, scattered frontal styles or 

 setae ; two rows of ventral setae ; no anal styles ; the marginal setae forming 

 a continuous projecting border. 



A single form is referred by Sterki * to this genus under the name of Stylonethes 

 tardus, but no specific description or illustration of it has as yet appeared. So far as 

 it is at present possible to determine, this single type connects the two genera 

 Holosticha and Uroleptus. 



GENUS XVI. ALLOTRICHA, Sterki. 



Animalcules free-swimming, soft and elastic, more or less ovate ; frontal, 

 ventral, anal, and marginal setae corresponding with those of Oxytricha 

 or Stylonychia, added to which are two supplementary rows of external 

 ventral setae as in Pleurotricha; structure of peristome, movements, and 

 general appearance coinciding with those of Urostyla. 



A single species, yet awaiting description, is referred to this genus by Sterki, f 

 under the title of A. mollis. 



GENUS XVII. PLEUROTRICHA, Stein. 



Animalcules free-swimming, persistent in form, elongate or elliptical, 

 with from five to eight claw-like frontal styles, the three anterior of which 

 are usually most conspicuously developed ; four or five scattered ventral 

 styles and in addition to these one or more supplementary rows of smaller 

 ventral setae ; anal styles five or six in number, forming two distinct groups ; 

 peristome-field not extending to the median line, its reflected border ciliate, 

 usually bearing a conspicuous, band-like, undulating membrane ; endoplas't 

 ovate, sometimes multiple ; contractile vesicle situated near the posterior 

 angle of the peristome. Inhabiting fresh water. 



While in its general characters this genus closely corresponds with Stylonychia, its 

 members are distinguished from the latter by the absence of caudal setae, by the 

 more luxuriant development of the ventral setae, and by the separation of the anal 

 styles into two distinct groups. 



Pleurotricha grandis, Stein. PL. XLIII. FIG. 26. 



Body elliptical, about twice as long as broad, peristome-field not extend- 

 ing to the median line, its reflected inner border ciliate, bent round towards 

 the opposite one at its distal extremity, the central area of the peristome- 

 field bearing a conspicuous line of endoral cilia ; the four or five sub-central 

 ventral uncini supplemented on each side by two parallel rows of smaller 



* 'Zeitschrift fur Wissetischaftliche Zoologie,' Bd. xxxi., 1878. t Ibid. 



