546 ORDER HOLOTRICHA. 



It is almost impossible to decide whether this species, briefly characterized as 

 above by Ehrenberg,* is rightly referable to the genus Cydidiiim, or even in such a 

 case whether, though smaller, it is specifically distinct from C. glaucoma. 



Genus III. URONEMA, Dujardin. 



Animalcules free-swimming, ovate or elongate, persistent in shape ; oral 

 aperture ventral, supplemented externally by an extensile trap-like mem- 

 brane or velum ; the general surface of the body covered with vibratile cilia ; 

 one or more long caudal setae developed at the posterior extremity. 



This genus is readily distinguished from Pleiironema and Cydidium by the 

 character of the appendages of the general cuticular surface, which, in this instance, 

 consist of flexible vibratile cilia in the place of stiff, hair-like setae. 



Uronema marinum, Duj. Pl. XXVII. Figs. 6o and 6i. 



Body elongate ovate, crenulate or rugose, from two and a half to three 

 times as long as broad, rather thicker posteriorly ; cilia of the general surface 

 of even length throughout, dispersed in parallel rows, about five of which 

 are exposed to view by the body as seen in profile; caudal seta equalling 

 the body in length ; contractile vesicle posteriorly located ; endoplast 

 spherical, subcentral. Length i-Soo". 



Hab. — Vegetable infusions in salt and fresh water. 



In its earlier condition this animalcule closely resembles the immature state of 

 Cydidium glaucoma, it possessing no trap-like membrane, which is an after develop- 

 ment. In some of the youngest examples observed, only the longer oral cilia 

 were visible, the general surface of the body being apparently completely naked, 

 closely corresponding, in this condition, with the figure given by Dujardin of his 

 marine Acoinia cydidium.^ Dujardin's Enchdys corrugatum,X again, an inhabitant 

 also of sea water, is likewise indistinguishable from the young of Uronema. The 

 extensile hood-shaped membrane in this species is smaller and far more difficult to 

 discern than in Cydidium or Pkuronema, the animalcules but rarely presenting the 

 profile view requisite for its conspicuous exhibition. Although most abundantly 

 developed in salt water, a form, agreeing in all essential details with the present 

 species, has been recently obtained by the author from fresh water. 



Genus IV. B^ONIDIUM, Perty. 



Animalcules free-swimming, persistent in form, elongate-ovate, or sub- 

 cylindrical ; the anterior border obliquely truncate, perforated by the oral 

 aperture, bearing circumferentially an extensile hood-like membrane or 

 velum. 



Bseoniditim remigens, Perty. Pl. XXVII. Fig. 64. 



Body elongate, subcylindrical, straight or more or less curved, from three 

 to four times as long as broad, the posterior extremity rounded, the anterior 

 one obliquely truncate, perforated by the oral fossa, and bearing an extensile 

 hood-like membrane or velum, whose width equals that of the breadth of 



* 'Bericht Akad. Berlin,' 1S53. 



t Dujardin, ' Hist, des Zoophytes Inliisoires,' pl. %ii. fig. 5, 1S41. 



% Ibid., pl. vii. figs. I la and II*. 



