BRITISH DESMIDIE.E. 131 



***=>:** Frond smooth ; front vieiv with divergwg processes divided at 



the apex. 



18. 8. brachiatum ; frond smooth ; front view with thick diver- 

 ging processes which are deeply bifid or trifid at the apex ; end view 

 with three or four rays. 



Staurastrnm bijidum, Ralfs, Annals of Nat. Hist. v. 15. p. lol. t. 10. f. 3 

 (1845) ; Trans, of Hot. Soc. of Fdlnborr/h, v. 2. p. 138. t. 13. (Not 

 Desmidiiim bifdum, Ehr., or P/u/castrum bifdum, Kiitzing.) 



Goniocystis {Staurastrum) bifdum, Hassall, Brit. Freshwater Alyce, p. 355 

 (1845). 



Dolgelley and Penzance, J. R. Near Bristol, Mr. Broome. Ambleside, 

 Mr. Sidebotham. Craigendurroch and Glen Lin, Aberdeenshire, Dr. Bichie. 

 Aberdeen, Mr. P. Grant. Reigate, Mr. Jenner. 



Frond minute, smooth, scarcely constricted at the middle, truncate at the 

 ends ; segments with three or four elongated, straight, tapering processes, which 

 are directed outwards, and consequently diverge from those of the other seg- 

 ment. In the front view each segment usually exhibits oidy two processes, 

 the others being hidden behind them. The processes are usually trifid at the 

 extremity, though sometimes merely bifid, in which latter case their diverging 

 points are forked like the tail of a swallow : the same bifid appearance may 

 occur in certain positions, even when three points are present. The end view 

 has three or four rays, hyaline, stout at their base, and gradually tapering. 

 In this view, as the frond is generally twisted, the rays of the lower segment 

 may be faintly seen between those of the nearer one. 



Sporangia have been gathered by Mr. Broome at Yate near Bristol ; they 

 are quadrate and spinous, and afPord the only known example of a quadrate 

 sporangium bearing spines. The emptied segments are easily detached ; the 

 spines are subulate and few. 



Staurastrum brachiatum may always be distinguished from S. paradoxum 

 and S. tetracerum by its smooth and divided processes. 



Length of frond jyt\ ^^ ^^^ iwch ; breadth yyVr 5 length of process from 

 tbVs *^ TiVs" ; length of sporangium from yqVo ^° tIt » length of spine from 



1 to -t 



2732 ''" 2048* 



Tab. XXIII. fig. 9. a. front view of frond ; b, c. dividing fronds ; d. end 

 \-iew of four-rayed variety ; e,f,g. sporangia. 



19. /S. l(£ve ; frond smooth; segments with short processes 



forked at the apex and directed outwards ; end view with three or 

 four bipartite angles. 



Pool near the outlet of Llyn Gwernan, Dolgelley, J. R. 



Fronds very minute, smooth, deeply constricted at the middle, the constric- 

 tion producing a wide triangular notch on each side. Segments externally 

 lunate or somewhat cuneate, but in general the outer margin is slightly protu- 

 berant at the middle. Each angle terminated by a pair of short, stout, hyaline 



K 



