394 Mr. J. Ralfs on the British Desmidiete. 



Fronds more or less granulated,, compressed,, deeply con- 

 stricted in the middle, the constriction forming a linear notch on 

 each side. In the front view the segments are broadest where 

 they are in apposition, and gradually narrower towards the end 

 where they are truncate ; consequently their figure is somewhat 

 angular. 



The end view is elliptic, as in C. margaritiferum and C. crena- 

 tum. 



Sometimes the pearly granules are very evident, sometimes 

 obscure. 



This species seems intermediate between C. margaritiferum and 

 C. crenatum, but may be distinguished from both by its truncate 

 ends. 



It may be known from C. ornatum by the elliptic end view. 



^ Plate XI. fig. 5. C. Botrytis : a, front view ; b, empty frond ; c, end 

 view. 



* Fronds not granulated, or the granules confined to the margin. 



6. C. crenatum. Fronds punctated, deeply constricted in the middle, 

 constriction forming a linear notch on each side ; segments com- 

 pressed, crenate at the margin. 



In bogs, small pools, &c. Weston Bogs near Southampton, and 

 several stations in Sussex, Mr. Jenner ; near Bristol, Mr. Thwaites ; 

 near Manchester, Mr. Sidebotham ; Dolgelley and Penzance. 



Fronds rather smaller than those of C. margaritiferum, deeply 

 constricted in the middle ; the close apposition of the segments 

 for their entire breadth renders the notch on each side linear ; 

 they are broader than long, compressed, crenate at the margin. 

 The end view is elliptic. 



This plant very much resembles a young specimen of C. mar- 

 garitiferum ; but as the margin is always strongly crenate, even in 

 the earliest stage, and the surface is punctated and not granu- 

 lated, I am induced to describe it as distinct. 



Plate XI. fig. 6. C. crenatum : a, front view; b, empty frond ; c, side 

 view ; d, transverse view. 



7. C. ovale. Fronds oval, compressed, punctated, deeply constricted 

 in the middle, the constriction forming a linear notch on each side ; 

 end view broadly elliptic. 



a. Segments entire at the margin. 



/3. Segments with marginal granules which give a dentate appear- 

 ance. Euastrum, no. 6, Bailey, /. c. p. 295. fig. 28. 



In boggy pools, a. Dolgelley, J. R. ; Barmouth, Rev. T. Salwey ; 

 near Tunbridge Wells, Mr. Jenner. 



(3. Weston Bogs near Southampton, Mr. Jenner. 



Fronds large, oval, slightly compressed, deeply constricted in 

 the middle, the constriction forming a linear notch on each side ; 

 end view broadly elliptic. The empty frond is punctated. 



