394 Mr. J. Ralfs on the British Desmidiere. 



Froiids 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 arc 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 kno^Ti from C. ornatum by the elliptic end \dcw. 



Plate XI. fig. 5. C. Botrijtis : a, front view ; h, 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 ; h, 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. 



ft. Segments with marginal granules which give a dentate appear- 

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

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



near Tunbridge Wells, Mr. Jenner. 



ft. Weston Bogs near Southampton, Mr. Jenner. 



Fronds large, oval, slightly compressed, deej)ly constricted in 

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

 end viev broadly elliptic. The empty frond is punctated. 



