786 ORDER HYPOTRICHA. 



GENUS XX. OXYTRICHA, Ehrenberg. 



Animalcules free-swimming, not encuirassed, more or less flexible and 

 elastic, ovate or elliptical ; bearing three or four uncinate and usually a few 

 supplementary setose frontal styles, five or more anal styles, a continuous 

 border of projecting marginal setae, and only a few, mostly five, scattered or 

 isolated ventral setae ; endoplasts two in number ; contractile vesicle single, 

 spherical, situated near the centre of the left-hand lateral border. Inhabit- 

 ing salt and fresh water. 



The genus Oxytricha, as amended in accordance with the foregoing diagnosis, 

 differs materially from the generic group bearing the same name as first originated by 

 Ehrenberg and included in all later works on the subject of the Infusoria. In 

 accordance with the recently published views of Wrzesniowski and Sterki, all those 

 forms characterized by the presence of two or more uninterrupted median rows of 

 short ventral seta? have been eliminated and referred to the new genus Holosticha, 

 from which latter again have been separated a third generic group bearing the 

 name of Amphisia, differing in the structure and disposition of the marginal setae, 

 which are scarcely to be distinguished from those of the ventral series. In the 

 considerable assemblage of forms yet remaining to represent the genus Oxytricha the 

 number and disposition of the few isolated ventral seta? correspond essentially with 

 the formula common to Stylonychia and Histrio, and from the latter of which two 

 genera Oxytricha is to be distinguished only by the soft and elastic instead of more or 

 less indurated character of the cuticular investment. The author has additionally 

 separated in this volume, as the type of the new genus Plagiotricha, the Oxytricha 

 strenua of Engelmann, which differs from all typical Oxytrichce in its possession of 

 two bristle-like caudal setae and an arrangement of ventral setae which most nearly 

 approaches that of Gastrostyla. 



Oxytricha pellionella, Mull. sp. PL. XLV. FIGS. 3-5. 



Body moderately elastic, not contractile, linear-elliptical, rather over four^ 

 times as long as broad, widest in the centre, the two extremities equally 

 rounded ; peristome-field narrow, triangular, extending to the centre of the 

 anterior third of the body ; no conspicuous reflected inner border ; ventral 

 setae represented by five irregularly disposed styles and setae only ; marginal 

 setae stationed at some distance from the periphery, the posterior ones only 

 projecting beyond its hinder border ; anal styles five in number, long and 

 stout, recurved towards the left, sometimes uncinate at their extremities, 

 and all projecting to a considerable distance beyond the posterior margin. 

 Length 1-288". HAB. Fresh water. 



This type corresponds with the Trichoda pellionella of O. F. Miiller. 



Oxytricha ferruginea, Stein sp. 



Body linear-oblong, about five times as long as broad, rounded and 

 widest posteriorly, the anterior end bluntly pointed, curved somewhat 

 obliquely towards the left ;. peristome-field wide, extending backwards to 

 the centre of the anterior third of the body, its inner border reflected to a 

 considerable distance and curved inwards to the left, bearing a distinct un- 

 dulating membrane ; median ventral setae represented by a few irregularly 

 disposed styles; marginal setae uninterrupted, projecting throughout the 



