394 MR. G. S. WEST ON 
on a definite system, although this is not readily discernible at 
first sight. There are always three or four large spines at each 
angle of the semicell and a lateral series, strongly developed, 
extending from angle to angle, as well as a more dorsal series 
also extending from angle to angle, those in the middle being 
as a rule (though not always) emarginate. Occasionally a few 
of the spines of the lateral series are duplieated, and the 
produced angles of the semicells possess encircling ringlets of 
minute denticulations. Any specimen which does not possess 
the above-mentioned characters cannot possibly be a form of 
Staurastrum aculeatum. l 
In 1872 Nordstedt described a var. ornatum of this species 
(* Desm. Spetsb.,” Ofvers. af K. Vet.-Akad. Forh. 1872, no. 6, 
p. 40, 0. 7. f. 27), and since that time much confusion has arisen 
with regard to certain allied forms. There can be no question 
that Nordstedt's variety is an extreme form of 8. aculeatum in 
which the lateral and dorsal series of spines have become more 
numerous and somewhat complicated ; but the arrangement of 
these spines is precisely similar to that in the typical form (as 
can be seen in Nordstedt's fig. 27 b). A few years subsequently 
to this Wille described some forms from Nova Zembla (“ Ferskv. 
Alg. fra Nov. Seml.,” Ofvers. af K. Vet.-Akad. Fórh. 1879, no. 5, 
pp. 54-55, t. 13. ff. 67-69) which he named S. aculeatum, Menegh., 
var. ornatum Nordst. forma spinosissima, and S. aculeatum var. 
depauperatum ; these belong undoubtedly to the same series of 
forms as S. sevcostatum and S. margaritaceum. Boldt has de- 
scribed a “forma simplex” of var. ornatum, Nordst. (“ Des. 
Grónl," Bih. till K. Sv. Vet.-Akad. Handl. Bd. xiii. Afd. iii. 
no. 5, p. 38, t. 2. f. 49), whieh is unquestionably a form of 
S. sexcostatum subsp. productum, West ; and Boergesen has also 
failed to comprehend the characters of S. aculeatum, having 
described a subsp. cosmospinosum of this species( Botan. Tidsskrift, 
Bd. xvii. p. 147, t. 6. f. 8) which is without doubt referable to 
S. rostellum, Roy et Biss. The list of confusing mistakes does 
not stop here, however, for we find forms of still more widely 
separated species referred to 8. aculeatum. One more instance 
will suffice: Schmidle has recently described (^ Lappmarks Süssw.- 
alg." Bih. till K. Sv. Vet.-Akad. Handl. 1898, Bd. xxiv. Afd. iii. 
no. 8, p. 55, t. 2. f. 44) a var. bifidum of S. aculeatum which 
certainly has no connection whatever with this species, but 
rather with S. forficulatum, Lund., and more particularly with 
