VARIATION IN THE DESMIDIER. 383 
var., Archer, in Quart. Journ. Mier. Sci. 1875, p. 414; var. 
tatricum, Raciborski, Pamietnik Wydz. Akad. Umiej. w Krakow. 
vol. x. p. 92, t. 13. £ 3; forma, Schmidle, in Oesterr. bot. 
Zeitschr. xlv. 1895, no. 7, p. 22, t. 16. f. 6, &c.; and I also 
give figures of some forms from widely separated localities 
(PI. 8. figs. 13-19) which will illustrate the considerable range of 
variation that is often met with. Some of these forms are more 
or less transitional between Huastrum affine, Ralfs, E. am- 
pullaceum, Ralfs, £. humerosum, Ralfs, and E. cuneatum, Jenner. 
5. MICRASTERIAS TRUNCATA, Bréb., in Ralfs, Brit. Desm. 
1848, p. 75, t. 8. f. 4, t. 10. f. 5.— This species, which was first 
described as Cosmarium truncatum by Corda in ‘ Almanach de 
Carlsbad, 1835, p. 150, t. 2. fl. 23-24, is probably the most 
generally distributed British species of the genus, and is often 
found up to considerable altitudes in mountain Sphagnum-bogs. 
It is equally widely distributed throughout continental Europe 
and North America, and for this reason it has frequently been 
made the subject of remarks by both English and foreign 
botanists. About twenty varieties have been described by 
different observers, many of which are not only connected with 
the typieal plant by series of intermediate forms, but also con- 
nected one with another by similar intermediate series. Perhaps 
the most interesting series of variations are those described 
and figured by Jacobsen in * Botanisk Tidsskrift, vol. viii. 1875, 
p. 152, t. 8. ff. 2-8. These figures alone show that the species 
is subjeet to very considerable variation, and an examination of 
any gathering in which it is abundant will afford ample evidence 
that this variation is of frequent occurrence. Adding to this 
the rather remarkable fact that forms met with from different 
loealities are rarely, if ever, identical in the extent and disposi- 
tion of their lobulation, it behoves one to make an exceptionally 
careful study of the species before definitely assigning a varietal 
name to any individual specimen under consideration. 
This is well illustrated by the figures I have given (Pl. 9. 
figs. 9-16) of eight specimens, each from widely separated 
localities, and drawn under the same magnification. They show 
the wide range of variation in outward form, in the extent of 
the lateral lobulation, the considerable differences met with in 
the nature of the lateral incisions, the disparity in size, and the 
variations in the comparative length and breadth of the indi- 
