and of equal diameter throughout. Colour a yellowish or greenish olive. 

 Substance tender, gelatinous and slippery. Fructification, elliptical spores 

 attached to the bases of the filaments of the periphery. Our variety, 0, 

 regarded by some authors as a distinct species, only differs in being of 

 smaller size, with less compound ramification ; there is no microscopic cha- 

 racter to distinguish it. 



An abundant species, on all our coasts, from the north of 

 Scotland to Cornwall, and subject to little variation except in the 

 amount of its ramification. Sometimes the branches are even 

 more densely set than our figure represents ; often they are more 

 distant, and occasionally the frond is very much less divided. In 

 the variety /3. especially, which grows on the leaves of the Zoster a, 

 the main stem seldom exceeds three or four inches in length, and 

 its branches are frequently rudimentary. I do not think, how- 

 ever, that it has sufficient characters to found a species upon. 



The appearance of a branch of this species under the micro- 

 scope is very beautiful, owing to the great length, and full greenish 

 olive hue of the filaments composing the periphery, which are set 

 in a looser gelatine than in any other of our British kinds, and 

 give the frond a singularly villous appearance, to the naked eye. 

 In this respect it differs from M. Griffithsiana which is of a much, 

 firmer and more compact substance. 



The Mesogloia affinis, of Berkeley, would appear, by the figure 

 and description, to be only the young of M. virescens; and 

 though I have not seen M. Hornemanni, Suhr., yet the descrip- 

 tion given of it by Kiitzing, accords so well with specimens of 

 M. virescens, communicated to me by Senator Binder, of Ham- 

 burgh, from Heligoland, that I have no hesitation in considering 

 it a synonyme. 



Pig. 1. Mesogloia virescens : — of the natural size. 2. Portion of the frond : — 

 slightly magnified. 3. Filaments of the periphery, and some of those of the 

 axis : — highly magnified. 



