Mr. J. Ralfs on the British Desmidiese. 405 



sometimes the celts seemed only held together by the hyaline 

 matrix, in which state they appear to connect the DesmidiecB, 

 through Gonidium, Ehr., and Trochiscia, Kutz., with the Ulvacece, 



The cells of one row are separated by the interposition of the 

 broader ends of the other. 



Plate XII. fig. 8. Sceneclesmns ohtusus. 



Desmidium*, Ag. {Kutz.) 



Filaments elongated, triangular or quadrangular, regularly twisted, 

 fragile ; the joints bidentate at the angles. 



In my former paper on Desmidium I removed from that genus 

 all Ehrenberg's species which do not form a filament, and re- 

 tained in it only those Des7nidiea which have elongated jointed 

 filaments. Since its publication, Kutzing, in his ' Phycologia Ge- 

 neralis,^ has restricted the genus to the species with triangular 

 filaments, and as this arrangement meets with the approbation of 

 Mr. Berkeley, I am induced, in deference to their joint opinion, 

 to follow it in the present article, with a slight alteration of the 

 character which will enable me to include the plant described 

 below. 



The transverse view is triangular or quadrangular, and the en- 

 dochrome has in one case three and in the other case four rays ; 

 these are frequently cloven. 



1 . D. Swartzii, Ag. Filaments triangular, equal, with a single lon- 

 gitudinal, waved, dark line formed by the third angle ; end view 

 triangular with the endochrome three-rayed. Kutz. Phycol. Ge- 

 neralis, p. 165 ; Menegh. Synop. Desmid. in Linnaca 1840, p. 203 ; 

 Ralfs in Annals of Nat. Hist. vol. xi. p. 375. pi. 8. fig. 3. 



I have only to add to my former notice of this plant, that it 

 has since been gathered near Cheshunt by Mr. Hassall, and in 

 many stations in Sussex by Mr. Jenner, also in Caragh Lake, 

 Kerry, by Mr. Andrews. 



2. D. quadrangulatum. Filaments quadrangular, varying in breadth 

 from the twisting of the filament, and having two longitudinal, 

 waved, dark lines ; the end view is quadrangular, with the endo- 

 chrome four-rayed. 



In a boggy pool at Bologas near Penzance. 



Mr. Berkeley and Mr. Borrer regard this plant as a variety of 

 D. Swai'tzii, nor can I find any distinctive mark except those 

 which depend upon the filament being quadrangular in one case 

 and triangular in the other ; but Mr. Jenner informs me that the 



* Read before tbe Botanical Society of Edinburgh, July 11, 1814. 



