6 Messrs. G. S. Brady and D. Robertson on the 
the two districts. But the theory of the efflux in bygone 
times of many of the rivers of northern Europe, including 
East Anglia, into one common estuary, though, no doubt, cor- 
rect, is scarcely sufficient to explain the identity of the two 
microscopic faunas to which we now invite attention ; for most 
of these peculiar species appear not to inhabit estuaries or even 
brackish water, but solely fresh water, which in many cases 
may be affected by the tides, but not sufficiently so to render 
it to any perceptible extent brackish. It is not likely, there- 
fore, that these species had their origin in any estuarine loca- 
lity, though doubtless such a means of communication may 
easily have helped to spread them from one district to another. 
Still it seems to us most oahs: that the real habitat of these 
species was at that early time, as it is now, almost entirely 
beyond the reach of marine eae, consisting perhaps of 
an extensive series of lagoons or low-lying fens surrounding 
the margins of the estuary, of which the present fen-districts 
of England and Holland are but the remnants. 
M. Félix Plateau has recently published a memoir on the 
freshwater Crustacea of Belgium, but does not mention any 
species identical with those new ones noticed by us in the 
East-Anglian district. It is probable, however, that his 
gatherings have been made entirely by the ordinary hand- 
net, in “which c case it is scarcely likely that any of our 
characteristic species would be obtained. In our own fen- 
gatherings, the dredged material only yielded the species to 
which we refer; though surface-gatherings were diligently 
made in most places visited by us, they yielded little or no- 
hing of special interest. The swimming ntomostraca taken 
in this way were all of purely freshwater character, and such 
as might have been found in any British waters of like extent. 
Our memoranda of these captures include the following spe- 
cies :— 
Teni pulex (Linn.). . Cypris reptans (Baird), 
vetula ( Müller). —— ovum (Jurine). 
DE mwa ah —— levis (Müller). 
—— rotundata (Strauss). — striolata, Brady. 
i lina ( Tüller}, — 7 
Polyphemus pediculus ( Zinn.) Cypridopsis 
osmin irostris (Müller) — aculeata ML 
Lynceus sph:ericus, Mi — em 
trigonellus, Müller. M 
—— quadrangularis, Müller. Limnicythere i inopinata ( Baird). 
—— harpe (Baird). —— trifica (Norn an). 
| — costatus (G. O. Sars). Gido pie varie). 
——— nanus (ani Canthocamptus wie ce (Ju- 
—— testudinarius, her. 
See ( Miller) Diaptomus € Castor ( Ataa 
«air = — Wes 
eai lamellatus (Müller). Argulus iei (Linn. * 
