352 DESMIDE^E. 



4. TRIGONOCYSTIS HEXACEROS Hass. 

 Plate LXXXIV. Fig. 11. 



Char. Fronds rough. Segments about twice as long as 

 broad, separated from each other by a deep notch, twisted. 

 End view triangular, with concave sides and blunt entire 

 angles. 



S. tricorne Meneghini, Synopsis Desmid. p. 225. Binatella 

 tricornis Breb., Alg. Fal. p. 57. (1835). Desmidium 

 hexaceros Ehr., Abhand. der Akademie d. Wissensch. 

 zu Berlin (1832), p. 292. ; Ehr. Die Infus. p. 141. t. x. 

 fig. 10. Staurastrum tricorne Kail's, in Annals, vol. v. 

 p. 155. pi. xi. fig. 2. ; Jenner, in loc. cit. p. 194. 

 Hab. Shallow pools, Piltdown Common; Ashdown Forest; 

 Rusthall Common ; between May field and Hadlow 

 Down : Mr. Jenner. Barmouth : Rev. T. Salwey. Dol- 

 gelly and Penzance : Mr. Ralfs. High Beech : A. H. H. 



" The conic granules arranged in transverse lines at the 

 angles are generally very minute, but in some Sussex spe- 

 cimens gathered by Mr. Jenner they are large, and on the 

 margin produce a dentate appearance." Ralfs. 



5. TRTGONOCYSTIS GRACILIS Hass. 

 Plate LXXXV. Fig. 1. 



Char. Fronds muricated, deeply constricted in the centre, two 

 or three times longer than broad, tapering on each side into 

 a slender process, which is terminated by three minute teeth. 

 End view triradiate. 



Euastrum No. 13. Bailey, in American Bacillaria, pi. i. 

 fig. 2 5. Staurastrum gracile Ralfs, in Annals, vol. 

 xv. pi. xi. fig. 3. 



Hab. Boggy pools, Dolgelly, and Penzance : Mr. Ralfs. 



Although but three processes or teeth usually present them- 

 selves to the observer, the real number is four ; but this is only 

 to be seen when one of the angles or rays is so situated that 

 its extremity is directly presented to the observer. 



