GENUS CHLOROPELTIS. 387 



This species was originally described by O. F. Miiller under the title of Cercaria 

 plcuronect's, it was transferred to that of Euglena by Ehrenberg, and to the present 

 one of Phacus by Dujardin. Examples figured in Stein's recently published volume 

 are represented as containing three or four large ovate sporosacs, his " Keimsacken," 

 or the so-called " glaire-cells " of Mr. H. J.' Carter, each of these enclosing an 

 endoplastule in an apparently unaltered state. 



Phacus triqueter, Ehr. sp. PL. XXI. FIG. i. 



Body ovate, compressed, leaf-like, having a raised keel-like elevation 

 produced down the centre of the right-hand side, presenting in transverse 

 section a triquetrous contour ; caudal prolongation one-fourth or one-third 

 the length of the body, acuminately pointed, directed obliquely towards 

 the .dorsal aspect ; cuticular surface finely but distinctly striate longitudi- 

 nally. Length 1-580". HAB. Fresh water, amongst Lemruz. 



Identical with the Euglena triqueter of Ehrenberg. 



Phacus pyrum, Ehr. sp. PL. XXI. FIG. 10. 



Body subfusiform or pyriform, about twice as long as broad, continued 

 posteriorly as a straight acuminate tail-like prolongation which equals or 

 slightly exceeds in length one-half of the preceding body portion ; cuticular 

 surface coarsely and obliquely sulcate. Length 1-1200" to 1-864". 



HAB. Pond water. 



First figured and described by Ehrenberg under the title of Euglena pyrum. 



Phacus longicaudus, Ehr. sp. PL. XXI. FIGS. 6 AND 7. 



Body ovate, compressed and leaf-like, often contorted or twisted upon 

 its axis, from one and a quarter to twice as long as broad ; produced 

 posteriorly as an acuminate, mostly straight, but sometimes irregularly 

 curved caudal prolongation, which nearly equals the body in length ; 

 cuticular surface finely striate longitudinally. Length 1-480" to 1-120". 



HAB. Fresh water. 



As explained by Stein in his index to the figures given of this species,* it is enabled 

 to change from the more normal flattened form to the screw-like or spirally twisted 

 contour, though in consequence of the comparatively hardened consistence of the 

 cuticle the process is very slow and gradual. In its power to alter in any way 

 its external configuration, this type differs essentially from the preceding species, 

 and may be said in consequence to occupy an intermediate position between the 

 typical members of the two genera Euglena and Phacus. The animalcule was 

 originally referred by Ehrenberg to the first-named genus. 



GENUS IV. CHLOROPELTIS, Stein. 



Animalcules free-swimming, persistent in shape, more or less ovate, 

 usually compressed, terminating posteriorly in an acuminate tail-like 

 prolongation ; oral aperture terminal, situated at the extremity of a short, 

 conical, snout-like prolongation, giving origin to a single, long, vibratile 



* ' Infusionsthiere,' Abth. iii., 1878. 



2 C 2 



