TKANSACTIONS. 
On the Genus Biddulphia and its Affinities. 
By F. C. S. Roper, F.L.S., F.G.S. 
(Kead May 19th, 1858.) 
The genus Biddulphia, one of the most interesting of all 
the class of Diatomacese, both from the generally large size 
and peculiar structure of the frustules, was one of the first 
of the minute class of Algse that attracted the attention of 
microscopists. Included by the earliest observers with a 
heterogeneous collection of other forms, differing widely in 
their structure, under the general title of Conferva, it was 
about fourteen years before its title to generic distinction 
was recognised, and then, together with the genus Fragillaria 
of Lyngbye, and the Diatoma of De Candolle, formed the 
whole of the order Diatomidese, enumerated in the ' Natural 
arrangement of British Plants^ of S. F. Gray. The genus, 
however, as formed by this writer, included only three 
species, B. pulchella, B. obliquata, and B. stipitata, which, 
as more attention was given to the lower class of Algae, 
were soon found to be widely different in their organization 
and modes of growth ; the first, however, has been ever since 
considered the type of the genus I am now about to de- 
scribe, whilst the second formed that of the genus Isthmia 
of Agardh, and the last was included by the same writer in 
the genus Achnanthes, as established by Bory. 
When Ehrenberg first began to pay attention to these 
microscopic forms, the constant succession of memoirs read 
before the Berlin Academy, induced a large number of 
microscopists, both here and on the Continent, to study with 
greater care the infinite variety and beauty of these minute 
plants, that had hitherto been almost unnoticed, except 
by a very limited number of algologists ; and from that time 
the genus Biddulphia has attracted a large share of atten- 
tion. The species, however, of which it is composed, being 
the most protean in their habits of growth of the whole 
order of Diatomacese, presenting even in the same localities 
very great variety both in form, size, and areolation of the 
entire frustules, and exhibiting such totally difi'erent appear- 
ances when only the separated valves are examined, that 
it has, during the last fifteen years, been divided and sub- 
divided, on slight, and I think quite untenable, grounds, into 
about eight or nine genera, including, in the various papers of 
Ehrenberg, Kiitzing, Bailey, and others, nearly sixty species. 
VOL. VII. h 
