BRITISH DESMIDIE^. 



* Plant an elongated jointed filament. Sporangia orbicular, smooth. 



1. HYALOTHECA, Ehr. 



Filament elongated, cylindrical, very gelatinous ; Joints having either 

 a slight constriction which produces a crenate appearance, or a 

 grooved rim at one end which forms a bifid projection on each 

 side. End view circular. 



The filaments are cylindrical, simple, jointed, invested with a broad 

 gelatinous sheath, and very fragile in one species but not so in the 

 other. Either a groove passes round each joint, giving a crenate 

 appearance to the margins of the filament and dividing the endo- 

 chrome into two portions, or else a grooved rim at one extremity of 

 the joint appears on each side like a bifid process. 



A transverse view shows a radiate endochrome in one species ; but 

 I have been unable to determine whether this occurs in the other, 

 on account of its imperfect fragility. 



The cylindrical filament distinguishes this genus from Desmidium 

 and Spharozosma. It has no angular projections, is not twisted, and 

 has always the same apparent breadth, and consequently in all these 

 respects differs from Didymoprium. 



I. H. dissiliens (Smith) ; filament fragile, crenate; a shallow groove 

 round each joint dividing the endochrome into two portions. 



Conferva dissiliens. Smith, Eyxg. ^o^ t. 2464. (1812) (not Dillw.). 

 Desmidium mueosum, 13reb. Aly. Fat. p. 65. t. 2 (1835). Menegli. St/nop. 



Desmid. in Litincea 1840, p. 204. Ralfs in A?mals of Nat. Hist. v. 11, 



p. 374. t. 8. f. 2. 

 Besmidium limbatum, Chauv. Alg.de la Norm. f. 6. (1836), according to 



Meneshini. 



