170 Mr. G. H. K. Thwaites on the Diatomaceae ; 
Found in small quantity in a rapid stream of fresh water on 
the filaments of Vaucheria, roots of grass, &c., at Crowds Hole 
near Bristol, in December last. 
Schizonema subcohcerens, n. sp. PI. XII. fig. G 1 (-]-), 2 (-^), 3- 
7 (y^). Cselomatibus in massam amorpham subcohaerentibus, 
valde mucosis, ramosis, navicularum ssepe multas singulas 
series continentibus : naviculis late truncatis, versus apices 
subito angustatis, striatis. 
Evidently closely allied to Schizonema ? mucosum, Kiitz. Bacill. 
115. tab. 26. fig. 9, but differs from it in having the frustules 
striated and towards the apices suddenly narrowed. Tufts of the 
plant from a quarter to half an inch or more high ; filaments very 
mucous and tenacious, and each containing from one to several 
single rows of frustules, which are continued without interruption 
into the branches. 
For the opportunity of figuring and describing this interesting 
species I am indebted to the kindness of the Rev. W. Smith, 
F.L.S., who found it in June last in Wareham North River,^^ 
densely spreading in a spongy stratum over the clayey bank and 
bottom of the stream. 
The sporangia of this species, fig. G 6, are produced by the 
conjugation of a pair of frustules outside the filaments ; but spo- 
rangial frustules are frequently found in a filament intermixed 
with ordinary frustules, from which they differ only in size : 
from this and from what has been observed by the writer in 
other species, it would appear that the frustules have a tendency 
to arrange themselves into linear series, and that subsequently a 
mucous sheath is developed around them. 
Schizonema subcohcerens would appear to belong to Agardh^s 
genus Micromega ” : it is difficult however to see the advantage 
of creating a new genus from characters derived from the mu- 
cous sheath only, and which characters really may be present in 
some species without being clearly evident. The so-called sper- 
matia of Micromega, now that the true sporangia have been 
discovered, require further examination : a somewhat similar ap- 
pearance to what ;s figured by Kiitzing is sometimes evidently 
due to minute zoophytes in an immature state. 
Schizonema vulgare, n. sp. PI. XII. fig. H I (y), 2-5 (Hp). Na- 
viculis Isevibus, lanceolatis, versus apices subito angustatis. 
Hab. in aqua dulci. 
Var. a. rivulorum. Fig. H 1-4. Cselomatibus distinctis, ra- 
mosis : naviculis subacutis. 
