356 desmidetE. 



2. Pentasterias margaritacea Ehi. 

 Plate LXXXY. Fig 7. 



Char. Frond rough. Segments in front view subglobose, at- 

 tenuated at their junction, icith short lateral converging 

 processes which are entire at their apices. End view loith 

 Jive, rarely six or seven, short obtuse rays. 



Staurastrum margaritaceum Menegh., Synops. Desmid. 

 p. 227. ; Ralfs, in Annals, vol. xv. p. 157. pi. xi. fig. 7. 

 Pentasterias margaritacea Ehr., Infus. p. 144. t. 10. 

 fig. 15. ; Jenner, in loc. cit. p. 194. 



Hab. Dolgelly : Mr. Ralfs. Ashdown Forest, Sussex : 

 Mr. Jenner. 



The rays are much stouter and shorter in this than in the 

 preceding species. 



3. Pentasterias Jenneri Hass. 



Plate LXXXY. Fig. 6. 



Char. Fronds large, dentated. Segments about as broad as 

 long, lengthened into a toothed angle on each side. End 

 view loithfive, sometimes six, broad short-toothed rays. 



Staurastrum Jenneri Ralfs, in Annals, vol. xv. p. 158. 

 pi. xi. fig. 8. ; Jenner, in loc. cit. 



Hab. Mayfield, Sussex : Mr. Jenner. 



A very fine species. " The transverse view has a large 

 central opening surrounded by a row of large granules." — 

 Ralfs. 



55. ARTHRODESMUS mr. 



Char. Fronds smooth, deeply constricted. End view com- 

 pressed, angles prolonged into a spine. 



Derivation, From dpOpov, a joint, and SsafMos, a link. 



The stout spines terminating the angles of the segments 

 seem to connect this genus with Xanthidium. 



