Mr. J. Rulfsj un the British Desmidiere. 151 



pears to have only three jiroccsses in a front view, whieh seems 

 to have nii-sled KUtzin^, wlio has made anotlier species of it. 

 The end view is nuich compressed, and tenninaled Ijoth ways by 

 an elonj^ated process. The frond is rovi^h witii minute granules, 

 which form transverse lines on the processes, and give them a 

 jointed appearance. The colouring matter is very pale. 



Ehrenberg and JMeneghini imite the " Micrasteri/is tetrucera" 

 of Kiitzing to the " Staurastrum jjaradoxumj" j\Ieyen ; but the 

 latter plant has four processes at each end, whilst the present has 

 only two, which, if 1 am con-eet in my view of the following spe- 

 cies, differ also in their entire extremities. 



Plate X. fig. 1. Staurastrum ietracerum : a, front view ; b, end view ; 

 c, side view, 



2. S. paradoxum, Meyen. Fronds rough; front view with elongated 

 diverging processes which are minutely trifid at the apex ; end 

 view quadrangular or sometimes triangular. Meyen, Nov. Act. 

 Leop. Holm. vol. xiv. p. 43. tigs. 37, 38; Menegh. Synop, Desmid. 

 p. 227. Micrasterias Staurastrum, Ktz. /. c. p. 599. 



In pools and slow streams, Dolgelley and Penzance. 



Fronds verj' minute, green, generally much constricted in the 

 middle, the ends truncate ; each segment has generally four elon- 

 gated processes diverging from the processes of the other seg- 

 ment. The end view is sometimes trilateral, but generally qua- 

 drilateral, and shows the angles elongated into rays ; I have also 

 seen a specimen in which one segment had four and the other 

 only three rays. In the front view the frond generally rests on 

 one of its sides, when each segment appears to have only two 

 processes, as the other two are covered by them ; sometimes only 

 one process is thus hidden, and occasionally all four may be seen 

 at the same time. The processes are elongated, coloui'less, and 

 being rough with minute granules airanged in transverse lines 

 acquire a jointed appearance ; each terminates in three minute 

 points. 



When only two processes are seen at each end in the front 

 riew, this species bears much resemblance to the preceding ; but 

 its frond is more constricted, larger, of a deeper green, and its 

 processes are thicker and not entire at the apex. 



In the newly -formed segment the processes are merely conical 

 projections. 



Plate X. fig. 2. .S". paradoxum: a, front view; h, newly-formed seg- 

 ment ; c, end view ; d, end view of new segment ; e, front and end views of 

 three-rayed variety. 



3. <S. bifidum. Frond smooth ; front view with thick diverging pro- 

 cesses which are deeply trifid at the apex ; end view triradiate. 

 Desmidium bifidum, Ehr. Infus. p. 141. tab. 10. fig. 11. 



In boggy pools : rare. Dolgelley and Penzance. 



