BRITISH DESMIDIE.E. 55 



mucous sheath is partially dissolved, and interferes with the examination of 

 the joints, but by repeatedly changing the Avater I succeeded in procurmg 

 many single joints. The transverse view was circular, and when the cell was 

 empty the border appeared decidedly striated. The endochrome had some 

 tendency to a radiate form, but the treatment to which the filaments had been 

 subjected prevented me from forming any certain conclusion as to its dispo- 

 sition in the recent plant. 



Under the microscope H. mucosa may be known from //. dissiliens by its 

 joints never appearing crenate, and by its endochrome being almost always m 

 a single patch, or by the greater length of the joints if the endochrome is bi- 

 partite. Its mucous sheath is with difficulty detected, and when seen will be 

 found to extend on each side twice the breadth of the coloured filament ; 

 whereas in H. dissiliens the mucous sheath is, except in old specimens, de- 

 tected without difficulty. 



The joints seem to be in pairs ; a single one is consequently unsymmetrical. 



n. mucosa agrees with the other Desmidiese in its capability of bemg kept 

 a long time without undergoing decomposition. 



This plant differs in many respects from the other Desmidiese ; indeed so 

 much so, that I had some doubts whether it would be correctly placed in this 

 family ; but as the Rev. M. J. Berkeley, as well as every other algological 

 friend whose opinion I have solicited, considers that its place must be in the 

 same genus with the preceding species, I have described it here. 



I was first indebted to Mr. Ilassall for the information that the plant mider 

 consideration is the Conferva mucosa, Dillw., as also for an opportunity of 

 examining a foreign specimen under that name from the herbarium of Dr. Gre- 

 ville. I have since been enabled to compare our plant with a portion of an 

 Irish specimen of Conferva mucosa presented to me by Mr. Borrer, who re- 

 ceived it from Sir W. J. Hooker. From the latter I learn that this was an 

 original specimen from Miss Hutchins. SirW. J. Hooker has also presented 

 me with an Appin specimen, collected by Capt. Carmichael. All these are 

 identical with the present plant. 



Length of joint from y^Vs^ to xtto ^^ ^" inch ; breadth of filament x^Vo ^^ 

 XTT\ 5 breadth of sheath j-^. 



Tab. I. f. 2. a. portion of a filament ; h. empty joints ; c, d. transverse 



2. DIDYMOPRIUM, Kutz. 



Filametit elongated, gelatinous, fragile, regularly twisted, cylindrical, 

 with a bidentate process or angle on each side of the JoinL 



The filaments are elongated, simple, jointed, gelatinous and very 

 fragile, and finally separate into single joints ; each joint has two op- 

 posite bidentate angles or processes. Hence the margins of the fila- 

 ment are crenate ; and as it is regularly twisted, it not only appears 



