248 DESCRIPTION OF [Poli/ffastnca. 



terias in having lobes and cmarginate ends, but the lobes are not 

 incised, nor do thoy radiate from the centre, and the inflated projec- 

 tions will distinguish it not only from Micrasterias, but from every 

 other genus in the family. From Cosmarium it differs also in the 

 lobed and emarginate segments. 



Ehrenberg's characters of this genus Euastrum, or star-dislced Ani- 

 malcules are — members free, inclosed in a simple compressed lorica, 

 composed of only one piece, and by their adhering in pairs, which 

 are disposed in the form of a two-lobed disc or table. Whether a 

 lobe can be regarded, separately from its companion, as a distinct 

 organism, is not determined, but by cutting or destroying the 

 one, the other empties itself at the same time, although the lorica 

 appears detached in the middle. No openings have been seen in the 

 ends, as in Micrasterias, but it is probable such exist in the middle, 

 where they are connected. The lorica is membranous, firm, colour- 

 less, and combustible ; it contains the hyaline and contractile 

 body of the animalcule, filled with green granules. Its propa- 

 gation by self-division is jjeculiar and highly interesting. (See 

 f. 123.) The middle elongates, and fi'om it two new segments are 

 formed, one uniting and forming the companion to one of the old 

 ones, and the other producing the same with the remaining old 

 one, when the newly-formed individuals separate, and two pairs 

 are the result. From this method of self-division, specimens having 

 unequal lobes, are produced by any accidental rupture, before 

 the new ones in the middle are fully developed. All the species are 

 found among conferva. 



Mr. Ralfs divides this genus into three sections. 

 1 . Segments of the frond deeiily hied ; terminal lole cuneate, and partly 

 included in a notch for med by the projection of the lateral lobes. 

 EuASTRUJi verrucosum (Ehr.) — Frond rough with conic granules; 

 segments three-lobed ; lobes broadly cuneate with a broad shallow 

 notch. Transverse view oblong, with three inflations at each side, 

 and a smaller one at each end. It is known by the conic granules 

 giving a dentate appearance to the outline. Length 1 -267th. 

 Breadth 1 -270th. (P. 2. f. 125.) 



U. oblongum = (E. pecten, Ehr.) — Smooth, oblong ; segments five- 

 lobod ; lobes cuneate, emarginate, the terminal one partly included 

 between the lateral ones. Empty fronds pimctate. Sporangia orbi- 



