On Homecrapia iv Fresn Warer. By F. L. EvLenstern, 
of Stuttgart. 
Tue majority of frond-bearing diatoms, constituting the 
Tribe II of Professor Smith, the status involucratus of Kiit- 
zing, are marine; still nearly every generic type of the tribe 
is found represented by a fresh-water form, and the cymbelloid 
type of frustule is even exclusively such. The fresh-water 
genus, Frustulia, Ebr., characterised by naviculoid frustules 
in a gelatinous stratum, may be said to prepare the way for 
the higher marine forms with definite fronds. Berkeleyia, 
Drokreia, and several species of that genus, are common on 
the continent. The higher Schizonemata are all strictly 
marine; but Colletonema affords a good fresh-water illus- 
tration on a lower scale, the latter genus being, however, much 
less known on the continent. Only this spring I have dis- 
covered C. vulgare, Thu., to be pretty frequent in the 
environs of Stuttgart, and it may have been often overlooked 
from its uncommon habitat, which, as far as my experience 
goes, is confined to deep mud, where it creeps below the films 
of Pleurosigma attenuaium, Pinnularia viridula, etc. Another 
species, C. viridulum, Bréb., has been found in. Silesia by 
M. Bleisch, who has accurately followed up its development. 
At first the frustules aggregate into small dark-brown com- 
pact heaps on a soft gelatinous stratum. From the latter, at 
the pomts where‘ the frustules aggregate, tubes are evolved 
which penetrate into the mud like the roots of a plant, and 
thus a Colletomena results which before any judge would have 
pronounced a Frustulia. From a series of specimens in his 
possession, M. Bleisch believes these genera to pass into each 
other without a definite line of demarcation. 
Passing over the genus Mastigloia, being distributed over 
both mediums, there only remains Homeecladia (with 
Raphdogloea, Kg.) possessing the nitzschoid type, which 
has not hitherto been observed in fresh water. From the 
great abundance of free Nitzschiz in almost every aquatic 
gathering, the absence of a fresh-water Homeecladia appeared 
the more striking, and it was with much gratification that a 
short time ago I succeeded in finding out the coveted plant. 
On examining cushions of Gomphonema curvatum from a 
waterfall in the neighbourhood of Stuttgart, I was struck by the 
appearnce of what seemed a Colletonema entangled between 
the stripes of the Gomphonema. Having placed a filament on 
