396 MR. G. $. WEST ON 
There are severai distinct varieties of this species :—var. de- 
nudatum, Nordst. (“ Desm. Brasil," Vidensk. Medd. nat. Foren. 
Kjóbenhavn, 1869, p. 230, t. 4. f. 40), in which the dorsal series 
of emarginate warts are much reduced ; var. semivestitum, West 
(Journ. Roy. Mier. Soc. 1892, p. 732, t. 9. f. 38) a small 
twisted form with only one of the fureate spines on each lateral 
margin ; and var. tortum, West & G. S. West (Journ. Linn. Soc., 
Bot. vol. xxxiii. (1898) p. 317, t. 18. f. 16), a larger form with 
curved processes twisted on their axes. 
Var. ornata, Istv. (in Notarisia, no. 5, 1887, p. 240), is de- 
seribed “ semieellulis dorso mucronibus bidentatis ornatis," but 
this is a charaeter of the typical form. 
18. STAURASTRUM FURCIGERUM, Bréb., in Menegh. ** Synops. 
Desm.,” Linnea, 1840, p. 226.—This species, first described by 
Brébisson as Binatella fureigera (m C. L. Chevalier, “Des 
Microscopes et de leur Usage,’ Paris, 1839, p- 272), belongs to that 
section of the genus Staurastrum characterized by the possession 
of a superior and an inferior whorl of processes. The typical 
form possesses three processes in each of the whorls, the superior 
processes being situated immediately above the inferior, and 
plaeed at an angle of about sixty degrees to them. It is often 
found in quantity in pools amongst Myriophyllum, Sphagnum, 
and Utricularia ; and in examining a large number of specimens 
from Birkhouse Moor Tarn, Helvellyn, and Pilmoor, near Thirsk, 
I was sufficiently fortunate to find one example from each locality 
which differed strikingly from the typical form. The superior 
whorl of processes of one semicell was duplicated, two processes 
being situated immediately above each one of the lower whorl. 
In one example (Pl. 10. fig. 35) the two semicells were equally 
developed, but in the other (Pl. 10. fig. 36) the semicell with the 
duplieated processes was more robust than the normal one, and 
the processes themselves much shorter aud differently toothed 
at their apices. 
In 1813, Ehrenberg (** Verbreit. u. Einfluss, mikr. Leb. Süd. u. 
N. Amer," Physik. Abh. Preuss. Ak. Wiss. Berlin, t. 4, f. 23) 
described Desmidium eustephanum ; this was referred five years 
later by Ralfs (Brit. Desm. p. 215) to Staurastrum as S, euste- 
phanum, and has since appeared under that name in several text- 
books (cfr. Archer in Priteh. Infus. edit. 3, 1852, p. 742, t. 2, 
f.3; Wolle, Desm. U.S. 1884, p. 147, t. 48. ff. 9-10; Cooke, 
