ILLUSTRATIONS OF BRITISH FUNGI. 
89 
and merit of the work. The attempt is an ambitious one, and it is 
sincerely hoped that it may not fail for lack of that small support 
which it seeks. Further particulars may be obtained from the 
Editor of this Journal. 
NOTES ON BRITISH DESMIDS. 
By M. C. Cooke. 
The most unique and interesting collection of Desmids made by 
Mr. A. W. Wills, in the neighbourhood of Capel Curig, during 
1880, renders some observations essential as a supplement to our 
list in “ Grevillea,” vol. viii., p. 121. 
In so far as the forms have yet been identified, this gathering 
contained no less than nearly ninety species, some of them new to 
the British Flora,” and many of them rare. 
Before commencing these observations, it will be necessary to 
give some explanation of our Plate 141. It will be remembered 
that in 1859 the Rev. R. Y. Dixon proposed Nat. Sci. Rev.,” 
vi., p. 464) a new genus, under the name of Tetrachastrum for such 
species of Micrasterias as were allied to M. oscitans, and described 
a new species under the name of Tetrachastrum mucronatum, of which 
our PI. 141, fig. 2 a is the typical form, or very nearly so. It was con- 
tended that this was a species quite distinct from Tetrachastrum 
oscitans, of which our fig. 2 / is a typical form. Having examined 
a collection made by Mr. A. W. Wills, in the neighbourhood of 
Birmingham, and a gathering from near Salisbury, we have found 
almost every intermediate gradation between these two extremes. 
So variable was the contour in the Birmingham gathering that no 
two individuals agree entirely with each other. From a large 
number of tracings by camera lucida we have selected only a few 
which are reproduced at PI. 141, fig. 2 to illustrate our view that 
there is in reality no specific difference. Fig. e, which was in 
company with fig. a, is more closely related to fig. /, which is T. 
oscitans, than to fig. a, which is T. mucronatum. Hence we regard 
all as forms of the same variable species. As to the genus Tetra- 
chastrum, let each be persuaded in his own mind ; for ourselves we 
do not recognize any very strong argument in its favour. 
Returning now to the Capel Curig gathering, we have to note 
the occurrence of Sphcerozosma i^Spondylosium) ‘pulchellum, Archer, 
a species hitherto only found in Ireland. 
Ot the species of Euastrum only one calls for special mention, 
and that approximates so closely to Euastrum erosum, Lund., that 
we do not hesitate to consider it a form of that species. Nothing 
can be more accurate and characteristic than the figures of 
Lundell, and we feel confidence in trusting to them, although in 
this instance we have seen no authentic specimen. 
