EUASTRUM. 379 



of numerous Closteria, and not differing from that of Stau- 

 rocarpus amongst the Co-njugatece. The steps of the form- 

 ation of this in Closterium and Tetmemoriis are as follow. 

 Two fronds coalesce, a cell is gradually formed between 

 them into which the endochrome passes from each frond 

 and which finally becomes moulded into a distinct organ or 

 sporangium invested with its membrane. 



61. EUASTRUM Ehr, 



Char. Frond compressed, deeply divided into tivo segments. 

 Segments longer than broad, usually pyramidal, emar- 

 ginate at their extremities, and lohed and tuherculated or 

 sinuated. 



Derivation. From sv, beautiful, and a(jTpov,.a star, 



" In this genus Ehrenberg includes Micrasterias Ag. (not 

 Micrasterias Ehr.^ and Cosmarium ; Meneghini separates the 

 former from it, but includes it in the latter genus. Euastrum 

 appears to me to be distinct from both, and especially from 

 Cosmarium. It agrees with Micrasterias in having lobes and 

 emarginate ends ; but the fronds are not incised, nor do the 

 lobes radiate from the centre. From Cosmarium it differs in 

 the lobed and emarginate segments, and also in the inflated 

 projections on the surface. These characters will also dis- 

 tinguish it from the other genera of this family." — Ralfs^ 



* 



a. Segments of the frond deeply lobed, tuberculated. Terminal 



lobes cuneate. 



1. Euastrum verrucosum Ehr. 

 Plate XCI. Fig. 7. 



Char. Frond denticulated. Segments three-lobed. Lobes 

 broad, suhcuneate, loith a broad shalloio notch between each 

 lobe. 



Euastrum verrucosum, Abhand. der Akademie d. AVissensch. 



* Annals, vol. xiv. p. 188. 



