171 
with descriptions of new genera and species. 
V^r. lacustre. Fig. H 5. Cselomatibus mucosis, simplicibus 
(aut parce ramosis ?) : naviculis latius truncatis quam in varie- 
tate prsecedenti. 
Monema lacustre, Agardh ? 
Var. 7 . effusum. Cselomatibus indistinctis^ in stratum gelatino 
sum eflusis : naviculis ut in varietate a. 
Although this is perhaps the commonest species of all the 
Schizonemata, since it occurs during the spring in almost every 
ditch and running stream, yet it does not appear hitherto to have 
been described, unless the Monema lacustre of Agardh should 
prove to be one of its forms. The speeies is most abundant in 
shallow streams, covering stones, &c. with a dark brown gelati- 
nous coating, but in which a linear arrangement of the frustules 
may frequently be detected. When the plant occurs in deeper 
water, the ordinary Schizonema filaments make their appearance, 
whieh are much-branched when growing in rapid streams, but 
when occurring in still water, or where there is only a slight cur- 
rent, are simple or nearly so. In the last-named form of the 
species, which may possibly be the Monema lacustre, Ag., there 
is also a slight difference in the form of the frustules, which are 
rather shorter compared with their width, and more truncated at 
their extremities. The frustules of all three varieties are of a 
lanceolate form, suddenly narrowed near the apices. 
Schizonema neglectum, n. sp. PI. XII. fig. J I {-j), 2-4 (^°). 
Cselomatibus ramosis, rnucosis : naviculis lanceolatis, delica- 
tule striatis. 
The filaments of this species, which are branehed, especially 
towards the base, easily escape detection owing to particles of 
sand and other substances adhering to their tenacious surface 
and being with difficulty removed from it. It is therefore next 
to impossible to get good examples of this species, and hence the 
reason why it has hitherto escaped the observation of botanists. 
The frustules are lanceolate and very delicately striated, and are 
very like those of Schizonema floccosum, Kiitz., which has been 
found by Dr. Dickie near Aberdeen ; but in that speeies they are 
not striated, and are moreover included in a gelatinous sheath of 
much greater thiekness than that of Schizonema neglectum. 
Occurring amongst other Diatomacece from fresh or slightly 
brackish water near Bristol. 
Diclcieia Danseii, TV. sp. PI. XII. fig. K I (^), 2-4 (y). Frons 
gelatinosa, indefinita, mammillosa : naviculis ovalibus, striatis. 
The frustules of this species are siliceous and of an oval form, 
