412 
MR. ROBERT GURNEY ON THE CRUSTACEA 
by rough chemical analysis between the salinity at high and 
low water at Acle. 
On the other hand, there are sometimes tides of exceptional 
height which drive the salt water up the river much further 
than Acle, and it is with the fauna of the river as influenced 
by these changing conditions that I propose to deal. The 
Tides, from both the Chemical and Physical standpoint, will, 
I hope, be dealt with fully at some future date. 
For the purposes of this paper I propose to divide the 
River Bure into three sections as follows : — 
(1) From Yarmouth to Six-mile House. 
(2) From Six-Mile House to Acle Bridge. 
(3) From Acle Bridge upwards, including the Ant and 
Thurne Rivers. 
No one section can, of course, be really divided sharply 
from the succeeding one ; but I think this method will be 
found convenient and satisfactory. 
Section I. — Yarmouth to Six-mile House. 
This section of the river may be considered as purely 
estuarine in character. The river is here a turbid stream 
with a very strong current both during flood and ebb. The 
banks are covered with the short grasses characteristic of 
salt marshes, and with abundance of the beautiful Aster 
tripolium. At low water the falling river lays bare consider- 
able stretches of sticky mud. The fauna is generally scanty 
and of a decidedly marine type, as the following collections 
will show. 
On the other hand, just as the salt water sometimes reaches 
far up the river, so there are times when the water is fresh 
right down to the river mouth. I have never met with quite 
such conditions myself, but I have seen a collection made by 
Mr. Eustace Gurney in April, 1901, at the Yacht Quay at 
Yarmouth which contained solely fresh- water species. At 
all times the floating fauna in this part of the river is exceed- 
ingly scanty. The water is thick with floating vegetable • 
debris and mud and generally contains very few individuals 
