GENUS UROLEPTUS. 779 



differentiated setose cilia ; ventral cilia disposed in four oblique spiral 

 parallel lines; a few scattered caudal setae developed at the posterior 

 extremity, and a row of similar marginal setae developed along the right- 

 hand border of the anterior body-half ; endoplasts axial, two in number, 

 with attached endoplastules ; contractile vesicle single, subcentral ; com- 

 pound tube or zoocytium pendulous, of granular consistence, branching in 

 an even dichotomous manner. Length of zooids 1-120", of branching 

 zoothecium 1-15" to i-io". HAB. Fresh water. 



GENUS XIII. STRONGYLIDIUM, Sterki. 



Animalcules free-swimming, elongate, soft and elastic, bearing about 

 six stout frontal styles, two oblique rows of ventral setae, three caudal, 

 but no anal setae ; the dorsal surface clothed with very fine, short, im- 

 motile, hispid setae. 



A single species, Strongylidium crassum, is briefly referred to by Sterki,* 

 as corresponding in general contour with Uroleptus piscis, but having a thicker, 

 almost cylindrical body, which is twisted upon its axis towards the left. The 

 large number of frontal styles, and the presence of caudal setae, would appear to be 

 the chief grounds upon which a new genus has been established for its reception. 



GENUS XIV. UROLEPTUS, Ehrenberg. 



Animalcules free-swimming, elongate, highly elastic, but maintaining the 

 same general contour; the posterior extremity usually produced in an 

 attenuate, tail-like manner ; the ventral surface bearing three or four anterior 

 or frontal styles, and usually two closely approximated median lines of ventral 

 setae ; a marginal border of similar setae continuous with or situated at a 

 little distance within the periphery ; no anal styles ; endoplast double or 

 multiple ; contractile vesicle single, spherical, located towards the posterior 

 termination of the peristome. Inhabiting fresh water. 



Uroleptus musculus, Mull. sp. PL. XLIII. FIG. 14. 



Body but little elastic, elongate-pyriform, three times as long as broad, 

 cylindrical anteriorly, dilated to its greatest width posteriorly, abruptly 

 rounded off in that region, and ending in a short, conical, tail-like termina- 

 tion ; the anterior end curved slightly to the left, the posterior one to the 

 right ; peristome-field extending backwards to about one-third of the length 

 of the entire body, its reflected border ciliate ; the border of marginal setae 

 encroaching considerably on the median area, projecting beyond the peri- 

 phery at the posterior extremity only ; central rows of ventral setae two in 

 number, produced to the extremity of the posterior termination ; anal 

 aperture located close to the base of the conical posterior termination; 

 contractile vesicle adjacent to the centre of the right lateral border. 

 Length 1-195" to 1-120". 



HAB. Fresh water, among Callitricha and other aquatic plants. 



* " Morphologic der Oxytrichinen," ' Zeitschrift fur Wissenschaftliche Zoologie,' Bd. xxxi., 1878. 



