OF THE EAST NORFOLK RIVERS. 
431 
more and more into operation with the rapid decrease of the 
tides, caused by the silting up of the estuary mouth, and the 
resulting shallowing of the Broads and rivers and lessening of 
the volume of water. 
Notes on Certain Species. 
The following notes may be regarded as supplemental to 
my list of 1903, so far as concerns the brackish-water species 
in the widest sense. I propose to give the names of all species, 
not already mentioned in my list, which have been found in 
the rivers from their mouths upwards and also to make a few 
remarks on certain species which are of special interest. 
MALACOSTRACA. 
Carcinus m.enas (Linn.). The Shore Crab. 
Crancon vulgaris (Linn.). Common Shrimp. 
Both these species appear to be strictly confined to the 
river mouths where the water differs little from sea-water. 
The latter is supposed to occur occasionally at Ludham Bridge, 
but, so far, I have no proof of it. 
Pal.emon squilla. Leach. White Prawn. 
This is a littoral species, sometimes found in estuaries. 
Mr. Patterson (‘Nature in East Norfolk,’ p. 334) states that 
it is often taken on Breydon. The only place in which I have 
met with it is Heigham Sounds, where a single large specimen 
was caught in one of my traps, perhaps the most remarkable 
capture I have made in the last four years ! 
Pal.emonetes varians (Leach). Ditch Prawn. 
When I wrote my list of East Norfolk Crustacea I had 
only found this species very rarely. Improved methods of 
capture show that it occurs commonly all the way up the 
Bure as far as South Walsham, and up the Thurne River as 
far as Potter Heigham. In the Waveney it is to be found 
as far as Oulton Broad. Mr. Balfour Browne has taken it 
in ditches in the neighbourhood of Horsey. Very likely 
it may prove to occur in Horsey Mere and possibly in Hickling 
Broad. 
