Mr. J. Ralfs on the British Desmidiese. 395 



• 



In the Welsh specimens I have always found the margin quite 

 entire, but in some sent me by Mr. Jenner the margin in the 

 front view is furnished with pearly granules which give it a den- 

 tate appearance, in which respect it agrees with a plant figured 

 in the ' American Bacillaria.' It appeared to me that the gra- 

 nules formed only a marginal band, and that the rest of the sur- 

 face was merely punctated as in the Welsh plant ; hence no gra- 

 nules were visible in a lateral view, and in an end one only at the 

 extremities. Mr. Jenner, however, finds the outline more or less 

 dentated in every view. In this variety the endochrome in each 

 segment is frequently divided into two portions by a longitudinal 

 pale line. 



When the margin is entire this species may be mistaken for 

 C. Cucumis, but the frond is oval, not orbicular, and when empty 

 is distinctly punctated. It is also much less compressed, the 

 transverse view being very different. 



Plate XL fig. 7. C. ovale : a, front view of empty frond ; b, side view; 

 c, transverse view ; d, front view of var. /3 ; e, empty frond with newly-formed 

 segment. 



8. C. Cucumis, Corda. Fronds orbicular, nearly plane, smooth, deeply 

 constricted in the middle, the constriction forming a linear notch 

 on each side ; end view elliptico-lanceolate. Menegh. I.e. p. 220. 

 Euastrum integerrimum, Ehr. Infus. p. 163. 



Boggy pools. Sussex, Mr. Jenner ; Dolgelley. 



Fronds orbicular, much compressed, quite smooth, deeply con- 

 stricted ; end view elliptico-lanceolate. 



The segments are quite entire at the margin, and I cannot 

 discover any puncta on the empty frond. 



Plate XI. fig. 8. C. Cucumis : a, front view ; b, empty frond. 



9. C. quadratum. Fronds deeply constricted in the middle ; segments 

 slightly compressed, quadrate in the front view. 



Rusthall Common near Tunbridge Wells, Mr. Jenner ; Dolgelley. 



Fronds constricted in the middle, and forming a short linear 

 notch on each side ; the segments are compressed, nearly square 

 in the front view, and at the base of each segment is a single 

 protuberance on each side. 



Plate XI. fig. 9. C. quadratum : a, a, front views; b, side view. 



10. C. Cucurbita, Breb. Fronds cylindrical with a slight constriction 

 in the middle, about twice as long as broad ; end view circular. 

 Cosmarium Cucurbita, Desm. no. 1103. 



Dolgelley, J. R.; Ashdown Forest, and Greatham Bogs near Pul- 

 borough, Mr. Jenner. 



Fronds very minute, cylindrical, rather more than twice as long 

 as broad, with a very slight constriction in the middle and rounded 

 at the ends ; transverse view circular with a large central opening. 

 The empty frond appears minutely punctated. 



