OF THE EXCHELIA. 



613 



Prorodon tiiveus. — Large, elliptical, 

 and compressed ; colour white ; circlet of 

 teeth compressed (teste Ehr.), as shown 

 separate in xxiv. 283. Smaller examples 

 have fewer teeth than the large. Cilia 

 very fine. It is fomid encysted. Amongst 

 Confervae in turf-pools. 1-72". Cohn 

 intimates (Zeitschr. 1853, iv. p. 271) that 

 this species and the next are merely 

 varieties of the same being. 



P. teres (xxiv.282j xxvni. 8). — Ovate, 

 cvlindrical, white ; circlet of teeth cylin- 

 drical. Ehrenberg coimted twenty sup- 

 posed teeth ; and when the cylinder was 

 broken, forty-five. Revolves, in swim- 

 ming, upon the long axis. 1-140". It 

 has been seen in the encysted state, and 



to undergo fission when in that condition. 



P. viridis. — Large, elliptic, compressed, 

 gTeen, with a nearlv cvlindrical crown of 

 teeth. 1-120". Berlin. 



In all probability this green-coloui-ed 

 organism is a mere variety of the pre- 

 ceding, from which it offers no distinc- 

 tive featm*es. In Prorodon, as in CJd- 

 lodon, fission occurs in encysted beings. 



P. vorax (Perty). — Hyaline, seldom 

 green ; dental apparatus faintly marked. 

 Integument covered with wart-like ele- 

 vations in rings. Movements tolerably 

 rapid ; oftentimes oscillating. Anus 

 placed at posterior extremity. 1-240" 

 to 1-84". It chiefly differs from P. niveus 

 by its faintly-marked dental apparatus. 



We have yet to append some genera (whose affinity is with the foregoing) 

 described by Dujardin, viz. Acomia, Gastrochceta, Alyscum, and Uronema, — 

 and which, vnth the genus Enchelys, constitute his family Enchelyens 

 (Enchelina). 



Acomia and Gastrochceta are only ciliated partially — the former at one 

 end, the latter along a longitudinal fiuTOW on the under surface. Enchelys, 

 Alyscum, and Uronema are ciliated throughout, — the first having but one 

 form of cilia ; the second, cilia together with some long, contractile, trailing 

 filaments ; and the last, cilia T\ith a single, straight and long posterior 

 filament. 



Genus ACOMIA (D.) (XXVI. 16, 17). — Oval or irregular, oblong, coloui-- 

 less or cloudy, formed of a homogeneous glutinous substance containing 

 unequal-sized granules, and ciliated at one end. No mouth. 



Perty remarks that there is an absence of definite characters between 

 this genus and the Enchelys (Duj.), and that the species of Acomia require 

 further study. 



Acomia CycUdium (xxvi. 16 a, b). — 

 Oval, oblong, depressed, containing large 

 granides and some vacuoles ; transverse 

 fission. In external form approaches 

 Cylidimn (Elir.). Marine, 1-650". 



A. vitrea (xxvi. 17 a, b). — Ovoid, hya- 

 line, but rendered cloudy by granules in 

 its posterior half ; anterior border ciliated; 

 division longitudinal. 1-1250". In fetid 

 water. 



A. ovalis. — Differs from the preceding 

 bv the gi-anules occup^dng the anterior 

 half, and by its length, 1-868". In fetid 

 marsh-water. 



The difference in position of the gra- 

 nules is valueless as a specific distinction 

 between this and the previous species, 

 and should be rejected. 



A. Ovulnm. — Ovoid, presenting a no- 

 dular or gi-anular portion, which seems 

 to contract itself within the interior 

 of a diaphanous envelope. Revolves in 

 moving, like a Doxococcus. 1-300". 



Stein (Iiifus. p. 137) declares that 



it is undistinguishable from CycUdium 

 Glaucoma (Ehr.). 



A. (?) Vorticella. — Ovoid, nearly glo- 

 bular, colourless, cloudy ; ciliated in its 

 anterior half; cilia curved backwards. 

 Revolves on its axis in progressing for- 

 wards. 1-1000". In sea-water. 



A. (?) costata. — Ovoid-oblong, nar- 

 rower in front ; apparently enclosed by a 

 thick membrane, or consistent layer; 

 nodular ; nodules often arranged in rows 

 as ribs. Division transverse. 1-650" to 

 1-500". In sea-water, among Algae. 



A. varians. — Oblong, cylindrical ; 

 truncated and angidar in front ; dilated 

 and compressed, by tiu-ns, in different 

 parts of its length, and consequently 

 alternately roimded and constricted be- 

 hind, so as to teniiinate by a pointed tail. 

 Revolves on its axis. l-l000"tQ 1-450". 



A. injlata. — O^al, tapering anteriorly, 

 beset every^vhere with very fine cilia; 

 colourless, or occupied with green, grey, 

 or brown granules. Movement rapid 



