VARIATION IN THE DESMIDIE E. 397 
Brit. Desm. 1887, p. 177, t. 62. f. 2). It differs from Staur- 
astrum furcigerum, Bréb., only in the duplicated superior whorl 
of processes, and, carefully considering this fact, Nordstedt 
(* Desm. frin Bornholm,” Vidensk. Medd. natur. Foren. Kjóben- 
havn, 1888, p. 207) placed it under S. Jurcigerum as forma 
eustephana. That he was qnite correct in so doing is at once 
evident from a consideration of the variation in the two specimens 
described above, in which one semicell represents S. furcigerum 
and the other A. eustephanum. It is quite certain, therefore, 
that S. eustephanum, Ralfs, must be regarded in the future as 
S. furcigerum, Bréb., forma eustephana, Nordst. I have ex- 
amined gatheriugs in which the form eustephana alone was 
present, but it is as a rule intermingled with the typical plant. 
Another form of this species is forma armigera, Nordst. (I. c.). 
This was first described by Brébisson as Staurastrum armigerum 
in Mém. Soc. Sei. Nat. Cherbourg, vol. iv. 1856, p. 136, aud 
subsequently redescribed by Reinsch as S. pseudofurcigerum 
in Abhandl. Naturhistor. Gesellsch. Nürnberg, 1866, Bd. iii. 
p. 169, t. 11. f. Z. It only differs from typical S. fureigerum in 
the duplication of the superior processes and in the slightly 
crenulate margins of all the processes, which have no small spines 
or granules. 
The ouly other notable variation exhibited by this species 
appears to be the occasional development of a very robust 
form, similar to the stout semicell in fig. 36, Pl. 10, but with 
only three superior processes. This form was deseribed as 
Staurastrum montanum by Raciborski (* Nonn. Desm. Polon.," 
Pamietnik. Akad. Umiej. Krakow., Wydz. matem -przyr. vol. x. 
1884, p. 90, t. 12. f. 11), and more recently deseribed as S. Surei- 
gerum var. erassum, Schröder (Forschungsberichten der Plöner 
Biol. Stat., Heft 5, 1897, p. 32, t. 3. f. 6). These two have 
been recently united, however, as S. Jurcigerum var. montanum 
(cfr. West & G. S. West in Journ. Bot. xxxvi. 1898, p. 335). 
19. ARTHRODESMUS CONVERGENS, Ehrenb., Infus. als vollk. 
Organism., Leipzig, 1838, p. 152, t. 10. f. 18.—This species ex- 
hibits a wide range of variation in the degree of development of 
the lateral spines. This is at once noticed on comparison of a 
specimen similar to that figured from Capel Curig, N. Wales 
(fig. 4, 5, p. 393), with one from Borrowdale, Lake District 
(fig. 4, a, p. 398). Examples are often found in which the spines 
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