BRITISH DESMIDIE^. 105 



22. C. commissurale (Breb.) ; segments narrow-reniform, three times 

 broader than long, rough with pearly granules ; end view with a 

 constriction between the central inflation and the extremities. 



Cosmariutn commissurale, Brebisson. Meneghini, Synop. Desmid. in Linncea 

 1840, p. 220. Brebisson, in lit. cum icone. 



Piltdown Common, Sussex, Mr. Jenner. Near Penzance, /. R. Near 

 Bristol, Mr. Thwaites. 



Falaise, Brebisson. 



Frond smaller than that of any other species in this section, broader than 

 long, very deeply constricted at the middle. The segments are compressed, 

 three times as broad as long, reniform, sometimes inclining to triangular in 

 consequence of the projection of the inflation at the margin ; they are rough 

 with pearly granules which give a dentate appearance to the outline. The 

 transverse view is three times longer than broad, with a constriction between 

 the central inflation and the rounded ends. 



The sporangia have been gathered very sparingly by Mr. Jenner. They 

 are orbicular, vdth slender, elongated spines, which are slightly di\'ided at the 

 apex and dilated at the base. 



The great breadth of the frond compared with its length and the reniform 

 segments well distinguish this species. 



Length of frond -^\^ of an inch ; greatest breadth -^^ to ^-i-g ; breadth at 

 constriction ^^^^g ; thickness of central inflation in end view y^^jy ; diameter 

 of sporangium j\^ ; length of spine of sporangium xaVs^* 



Tab. XVI. fig. 8. a. front view of frond; b. empty frond; c. transverse 

 view ; d. sporangium. 



23. C. cristatum ; frond orbicular, deeply constricted at the 



middle, margined by papilla-like pearly granules ; end view linear, 

 with an inflation at the middle of each side. 



Ambleside, "Westmoreland, Mr. Sidebotham. 



Frond exactly orbicvilar, much compressed, deeply constricted at the middle, 

 the constriction forming a linear notch on each side ; the segments margined 

 by a series of obtuse, papilla-like, pearly granules. At the centre of each 

 segment is a circular granulate inflation. The end view is nearly linear, with 

 truncate ends and an inflation on each side at the middle. 



The above description is foimded on INIr. Jenner' s notes and drawings. I 

 have not seen this plant, but have no doubt that it is a good species. 



Length of frond -g-i^ of an inch ; greatest breadth ^-i-j ; breadth at con- 

 striction xrrs' 



Tab. XVII. fig. 2. a, front view of mature frond ; b. empty frond ; c. end 

 view. 



