Ostracoda and Foraminifera of Tidal Rivers. 3 
(perhaps also, to a smaller extent, Loxoconcha) may be con- 
sidered especially littoral or estuarine in habitat; ; the elon- 
gated subsigmoid forms of Cythere (typified by C. pellucida) 
come also under the same catego 
The situations which seem to be most favourable to the 
growth and multiplication of these animals are quiet sheltered 
pools which are never left entirely dry by the tide, are un- 
swept by strong currents, and thus able to retain penoy 
a bed of soft mud. Many species there are, of course, whic 
prefer different conditions ; but it is in such localities that we 
and sc of species. A remarkably fine gathering, taken 
from a place such as we have described is that from the river 
Blyth (N orthumberland), which contained thirty-eight species 
of Ostracoda and thirty- ‘eight of Foraminifera. Budle Bay, 
on the same line of coast, with a harder bottom and more sub- 
ject to the wash of the sea, and also with much less admixture 
of fresh water, contained, as shown in our gathering, only 
twenty-six species of Ostracoda and thirty-six of Forammifera; 
while the river Coquet and the Warn burn, with much harder 
beds, stronger currents, and but little admixture of salt PEE 
gave respectively ten and six species of Ostracoda, and no 
Foraminifera. 
The Entomostraca of the tidal waters of Norfolk, -n 
and the Cambridge fen-district constitute so remarkable 
group that it seems best to speak of them separately ; and in 
so doing we shall call the area to which we refer the Hast- 
Anglian district, understanding by that term the whole tract 
drained by the rivers Nene, Cam, Bure, Yare, and Waveney. 
The drainage-tract of the adjoining rivers on the south, Ald, 
Deben, Stour, &c., is separated by rising ground, and appears 
to be zoologically distinct; but whether the more northern 
fen-district of Lincolnshire be likewise distinct, we have not 
= had the degere of examining. 1f, as is "probable, the 
tracts were in former times one continuous fen, we shall 
debidas find an indiċation of it in the similarity of their 
microscopic faun 
It is well nd that the present physical condition*of East 
Norfolk is of very recent origin. Only a few centuries back, 
the ground on which Great Yarmouth now stands was a s sand- 
bank covered by the sea; and the extensive tract between 
Yarmouth and Norwich was a shallow estuary, the gradual 
silting-up of which has produced the present physical con- 
formation of the district. "Through this extensive flat, whic 
lies below the level of the sea, now flow in tortuous channels 
the rivers Bure, Yare, and Waveney; and connected with 
1” 
