GEXUS 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 setas 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 setse, three caudal, 



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



motile, hispid setae. 



A single species, Strctigyhdium crasstim, is briefly referred to by Sterki,* 

 as corresponding in general contour with Urokptus 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 seta;, would appear to be 

 the chief grounds upon which a new genus has been estabhshed 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, Miill. 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 

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

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

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

 phery at the posterior extremity only ; central rows of ventral setJe 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. 



• ".MorphologiederOxytrichinen," 'Zeitschrift fur Wissenschaftliche Zoologie,' Bd. xxxi., 1878. 



