GENUS UROCENTRUM. 64 1 



Journal of Microscopical Science' for the year 1868, under the title of Ccenomorpha 

 convoiiifa, here reproduced at PI. XXXIII. Figs. 1-3, is evidently identical with 

 Stein's type. His brief account of the species, though it leaves much yet to be 

 recorded concerning this remarkable form, supplies some additional data of 

 importance. The body as described by this later observer, and as delineated at 

 Fig. I, is colourless, smooth, and conical, the anterior extremity curved somewhat 

 downward, and the posterior margin fringed at its edge with long, close-set cilia. 

 The tail-like portion is swollen at its base, somewhat eccentric, is as long or longer 

 than the body, and tapers to a point which is curved slightly upwards at its distal 

 extremity. In addition to its swift natatory mode of progression, Mr. Tatem relates 

 that from twelve to twenty of the cilia on the ventral surface present the character of 

 long stiff set^, and that with their aid the animalcule is enabled to creep over the 

 surface of algje or other submerged bodies ; the tail-like style is likewise described by 

 him as being sometimes bifid. The character and position of the oral aperture were 

 not determined, nor are any details recorded concerning the nature of the contractile 

 vesicle and endoplast. The former structure, although not recognized as such in 

 Mr, Tatem's description, is clearly indicated in his drawings in the same locality 

 first ascribed to it by Stein. Representations of a supposed earlier condition of this 

 organism are given by Mr. Tatem, one of which, PI. XXXIII. Fig. 2, excepting 

 for the position of the ciliary wreath, corresponds remarkably with. Perty's figures 

 of Ccenomorpha mcdusiila. This circumstance suggests the possibility that Perty 

 grounded his description of the last-named species upon young and certainly very 

 imperfectly observed examples of the present form. To complete the record of this 

 puzzling Peritrichous form, it is desirable to add that it is figured by Dr. Ernest 

 Eberhard in the ' Osterprogramm der Realschule zu Coburg ' for 1862, under the 

 title of Stronibidium polyiuorphiun, and there associated wath Metopus sigmoides, which 

 is regarded by him as merely its earlier or larval condition. This presumed affinity 

 is referred to at greater length in the account given of the last-named species. 



The diagnosis and more characteristic figures of Perty's Ccenomorpha medusiila 

 are herewith reproduced, and should future investigation successfully establish the 

 identity of the two, this authority's generic and specific title will, in accordance 

 with the laws of priority, have to supplant that of Stein's. So far as can be at 

 present decided, the author is inclined to regard the species as distinct, but the 

 genus identical. 



Ccenomorpha Jtiedusula, Perty. PI. XXXIII. Figs. 26-28.— Body colourless, 

 trabsparent, bell-like or hemispherical, its surface sometimes plicate, the base concave 

 and truncate, with an irregularly notched border ; a tail-like process comparable to 

 the clapper of the bell depending from the centre of the body; the margin of the 

 bell fringed with long cilia, which sometimes present the aspect of an undulating 

 membrane. Movements swift, rotating on its longitudinal axis. Length, with tail, 

 1-240" to 1-192". Hab. Standing water. 



Genus II. UROCENTRUM, Nitzsch. 



Animalcules free-swimming, ovate or pyriform, persistent in shape ; 

 body encircled by one or two circular girdles of cilia, and traversed on its 

 ventral surface by a longitudinal groove or furrow ; oral aperture ventral, 

 perforating the centre of the more posterior ciliary girdle ; an apparently 

 stylate, but more or less flexuose and adherent, caudal appendage pro- 

 duced from the posterior region of the body ; endoplast and contractile 

 vesicle conspicuously developed. Inhabiting salt and fresh water. 



Urocentrum turbo, Miill, sp. Pl. XXXIII. Figs. 7-10. 

 Body unevenly pyriform, largest and inflated anteriorly, constricted 

 centrally, narrower and triquetrous posteriorly, the ventral surface somewhat 

 VOL. II. N 



