BRITISH DESMIDIE^. 105 



22. C. commissurale (Br^b.) ; segments narrow-reniforrrij three times 

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

 constriction between the central inflation and the extremities. 



Cosmarium commissurale, Brcbisson. Meneghini, Synop. Desmid. in Linncea 

 1840, p. 220. Brcbisson, iti lit. cum icone. 



Piltdowii Common, Sussex, Mr. Jenner. Near Penzance, J. R. Near 

 Bristol, 3Ir. Thwaites. 



Falaise, Brcbisson. 



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, vrith a constriction between 

 the central inflation and the rounded ends. 



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

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

 apex and dilated at the base. 



Tlie 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 -g-ig^ ; breadth at 

 constriction yiVs" » thickness of central inflation m end view y\TT '■> diameter 

 of sporangium y^ ; length of spine of sporangium yaV^* 



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 orbicular, much compressed, deeply constricted at the middle, 

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

 hy 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 founded on Mr. 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-^-g of an inch ; greatest breadth ^^ ; breadth at con- 

 striction XT&5' 



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

 view. 



