192 Mr. J. Ralfs on the British Desmidiese. 



projections at each end and three on each side, and a small central 

 opening at the original junction-point of the segments. In the 

 specimens I gathered the terminal notch was but slightly marked, 

 partly perhaps on account of their immaturity, since in all the 

 species it is obscure in the young frond ; I doubt however whether 

 it is ever so remarkable in this as in the other species*. 



This plant agrees in its decanter-like form with the two pre- 

 ceding species, but I cannot suppose it to be a variety of either ; 

 for in this genus the projecting parts are much less developed in 

 the young than in the adult plant, and nevertheless they were 

 more evident in my immature specimens than in either of the 

 other species. 



Whilst engaged in examining this species, I was first struck 

 with the advantage to be derived from the figure of the transverse 

 view in the discrimination of nearly allied species. I have since 

 obtained Meneghinr's Synopsis of this family, and find that he 

 has extensively availed himself of it in forming his specific cha- 

 racters of this genus. 



Plate VII. fig. 4. Euastrum gemmatum : a, front view; b, side view ; 

 c, transverse view ; d, end view ; e, end view of terminal lobe ; /, var. /3. 



*** Segments with the end acute at the corners, or with acute lateral 

 processes. 



7. E. rostratum. Basal lobes of the segments broad and emarginate, 

 terminal lobe with a curved, acute, spine-like process on each side. 

 In fresh- water pools near Dolgelley. 



Frond very minute, about twice as long as broad ; segments 

 obscurely three- lobed, or rather with a broad base which is emar- 

 ginate at each side, and then contracted into a broad short neck 

 connecting it with the terminal lobe. The terminal portion has 

 on each side a curved subacute tubercle or process, somewhat like 

 a beak ; the end of the lobe is prominent, generally angular, with 

 a deep rounded terminal notch. 



This species, like the last, is contracted, but less decidedly, into 

 a broad, very short neck, and has emarginate sides, but differs 

 from it in its much smaller size, and especially in having acute 

 projections at the sides of the terminal portion. As in these re- 

 spects it approaches the two following, it seems to connect them 

 with the preceding species. 



Plate VII. fig. 5. Euastrum rostratum. 



8. E. spinosum. Fronds oblong ; segments obscurely lobed, with a 

 spine-like process on each side near the extremity ; the end pro- 

 tuberant and rounded. 



In fresh-water pools. Cheshunt, Mr. Hassall; Barmouth, Rev. T. 



* I have since examined mature specimens and found the terminal notch 

 always obsolete. 



