Myr. J. Ralfs on the British Desmidiece. 11 
with either a slight constriction which produces a crenate ap- 
pearance, or a grooved rim at one end which forms a bifid pro- 
jection on each side. 
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 endochrome into two portions, or else a grooved rim at one 
extremity of the jomt appears on each side like a bifid process. 
A transverse view shows a radiate endochrome in one species, 
but m the other I was unable to obtain this view on account of 
its want of fragility. . 
The cylindrical filaments distinguish this genus from Desmi- 
dium and Spherozosma. From Didymoprium it differs in the 
absence of angular projections, in not being twisted, and in al- 
ways having the same apparent breadth. 
1. G. dissiliens. . Filaments fragile, crenate ;.a shallow groove round 
each joint divides the endochrome into two portions. Desmidium . 
mucosum, Breb. Alg. Fal. p. 65. pl.11; Menegh. Synop. Desmid. 
in Linnea 1840, p. 204; Ralfs in Annals of Nat. Hist. vol. xi. 
p. 374. pl. 8. fig. 2. 
This plant is apparently common, as, in addition to the habitats 
already given, Mr. Jenner has gathered it in numerous stations 
both in Sussex and in Kent. It has also been gathered in Ire- 
land, near Bandon, by Dr. Allman, and in Kerry by Mr, Andrews. 
In an advanced state it becomes of a pale opake green, 
The mucous sheath is easily perceived, and is on each side of 
the filament as broad as the central coloured portion. The en- 
dochrome is divided into two portions by the central constriction, 
which can always be detected on a careful examination with the 
higher powers of the microscope. 
This plant has been involved in much confusion ; it was by 
mistake figured in ‘Eng. Bot.’ for the Conferva dissiliens of 
Dillwyn, and afterwards altogether omitted im Hooker’s < Br. 
Flora’ and in Harvey’s ‘Manual of the British Algz.’, From 
the synonyms in Meneghini’s ‘ Synopsis Desmidiearum,’ it seems 
that De Brébisson considered it the Conferva mucosa of Mertens 
and Dillwyn. 
2. G. mucosum. Filaments scarcely fragile; joints not constricted, 
but having at one of the ends a minute bidentate projection on 
each margin, the adjoining end of the next joint bearing similar 
projections. Conf. mucosa, Mert. ; Dillw. Brit.Conf. tab. B. ; Hook. 
Br, Fl. vol. xi, p. 851; Harv. Br. Alg. p. 127... Gloeotila monili- 
formis, Kutz. Phyc. Generalis, p. 245? 
In shallow pools and gently-flowing streams, probably not uncom- 
