422 MR. ROBERT GURNEY ON THE CRUSTACEA 
but such specimens are rather to be considered as comparable 
to the migratory birds which occasionally straggle to our 
islands outside their ordinary range. 
On the other hand, when exceptionally high tides bring 
salt water up the river, such salt water may reach up beyond 
this point and up the Ant. Unfortunately I have never been 
up the Bure at such times, so cannot say how far the salt can 
be traced in that direction, but I know that a rise of salinity 
may be detected, in these circumstances, as far as Barton 
and Sutton Broads. The rise of salinity at Sutton may 
amount to about 3 grs. per gallon. But even in circumstances 
of this kind it does not appear that marine floating species 
extend much further than Thurne Mouth. For instance, on 
July 13th, 1903, when several marine Calanoids and living 
Ctenophores (Hormiphora) were found at Thurne Mouth, 
the fauna at Ludham Bridge and in South Walsham Broad, 
though more scanty than usual, was of the usual type, with 
the exception that Neomysis vulgaris occurred at Ludham 
Bridge. I have been told several times that “ Brown Shrimps” 
( Crangon vulgaris ) are to be taken at Ludham" Bridge on such 
occasions, but I have failed entirely to find them myself, 
there or anywhere above Yarmouth, and have offered a reward 
for them in vain. It is quite possible that they do occur ; 
but I think that such statements may really refer to Palce- 
mov.etes varians. 
So far as concerns the Thurne River, I think the same holds 
good. That is to say, its fauna is only quite exceptionally 
affected by salt water from the sea. On the other hand the 
salinity in this river differs from that in the Bure in that it 
increases from the mouth upwards owing to water of high 
salinity flowing down from Hickling Broad and Horsey Mere 
where there must be salt springs. The result is that the fauna 
is comparatively scanty, and such species as Eurytcmora 
afjinis and Tachidius littoralis are found throughout its course 
and in the Broads themselves. Neomysis vulgaris and 
Gammarus duebeni do not, I believe, ordinarily occur in the 
river itself below Potter Heigham, though it is possible that 
they have been overlooked, but both are to be found in 
