Mr. J. Ralfs on the British Desmidiese. 13 



is of an opake green. The latter if kept in water for a few days 

 spontaneously separates into fragments ; G. mucosum, although 

 treated in the same manner for weeks, has not separated into 

 fragments sufficiently small to enable me to obtain a transverse 

 view. I am therefore unable to say whether the endochrome in 

 that aspect appears stellate, as in G. dissiliens. 



Under the microscope G. mucosum may be known by the joints 

 not appearing crenate and by the endochrome being in a single 

 patch, or if divided, the joints are longer than in G. dissiliens. 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 G. dissiliens the mucous sheath is, except in 

 old specimens, detected without difficulty. 



This is a remarkable plant, and differs in many respects from 

 the other Desmidiece ; 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 solicited, considers that its place must be in the 

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



The joints seem to be in pairs, and a single one is consequently 

 unsymmetrical. 



G. mucosum agrees with the other Desmidiece in its capability 

 of being kept a long time without undergoing decomposition. 



I was indebted to Mr. H assail for the information that the 

 plant under consideration was the Conferva mucosa, Dillw., as 

 also for an opportunity of examining a foreign specimen under 

 that name from the herbarium of Dr. Greville. 



I have since been able to compare our plant with a portion of 

 an Irish specimen of Conferva mucosa presented to me by Mr. 

 Borrer, who received it from SirW. J. Hooker. From the latter 

 I learn that this was an original specimen from Miss Hutchins. 

 Sir W. J. Hooker has also presented me with an Appin specimen 

 collected by Capt. Carmichael. All these are identical with the 

 present plant. 



Plate HI. fig. 6. GlcBopriiim mucosum : a, portion of a filament much 

 magnified to show the bifid projections ; b, less magnified to show the 

 breadth of the sheath. 



SpHiEROZosMA, Cordtt. 



Filaments gelatinous, plane, fragile ; joints closely united by 

 means of glandular processes, and deeply divided on each side, 

 thus forming two segments and giving a pinnatifid appearance 

 to the filament. 



The filaments are pale green, gelatinous, simple, plane, have a 

 pinnatifid appearance from the division of the joints into two 

 segments, are fragile, and finally separate into single joints. I 



