354 DESMIDE.E. 



Desmid. p. 227. ; Ralfs, in Annals, vol. xv. pi. xi. 

 fig. 5.; Jenner, in loc. cit. p. 194. 



Hah. Rusthall Common, near Tunbriclge Wells; and 

 Rackham Common, near Pulborough, Sussex : Mr. 

 Jenner. Dolgelly : Mr. Rolfs. 



The angles in this species are not as in the others prolonged 

 into rays, and this will at once serve to distinguish it from 

 those species. 



2. StAURASTRUM ? TETRACERUM Ralfs. 



Plate LXXXIV. Fig. 4. 



Char. Frond rough. Segments but slightly constricted, qua- 

 driform. Outer angles prolonged into diverging rays 

 tvhich are entire at their extremities. End view com- 

 pressed, with a process at each extremity. 



Staurastrum paradoxum Ehr., Infus. p. 143. t. 10. fig. 14, 

 Micrasterias tricera and tetracera Kiitz., Synops. Desmid. 

 in Linnaea, 1833, p. 602. figs. 83, 84, 85.; Ralfs, in 

 Annals, vol. xv. pi. x. fig. 1. 



Hah. Dolgelly and Penzance : Mr. Ralfs. 



The minute granules with which the frond is covered form 

 transverse lines on the rays, and give them a jointed appear- 

 ance. This species, in its compressed ellipsoidal form in the 

 end view, would appear to approach closely the genus Ar- 

 throdesmus. 



3. Staurastrum paradoxum Meyen. 

 Plate LXXXV. Fig. 3. 



Char, Fronds rough, constricted. Ends truncate. Front view 

 elongated, diverging processes minutely trijid. End view 

 usually quadrangular, hut sometimes triangular. 



Meyen, Nov. Act. Scap. Holm. vol. xiv. p. 43. figs. 37. 38.; 

 Mencgh. Synops. Desmid. p. 227. Micrasterias Staur- 

 astrum Kiitz., in Linnaia, p. 399. ; Ralfs, in Annals 

 vol. XV. p. 151. pi. X. fig. 2. 



