652 MR. R. GURNEY ON FRESH- AND BRACKISH-WATER CRUSTACEA. 
Microdeudopus gryllotalpa, Costa. A few specimens were 
taken by Mr. K. A. Todd in Ploughman’s Ham by 
Lake Lothing. 
DISTRIBUTION. 
In the above table,* I have summarised the main facts of distri- 
bution within the Broads district ; but the table requires some 
explanation and amplification. I have only included in it such 
Broads and stations as have been more or less completely worked, 
and the records given for each Broad are supposed to refer not only 
to the Broad itself, but also to the ditches immediately connected 
with it. 
It was hoped at the outset that considerable differences might 
be found to exist between the faunas of the different Broads, cor- 
responding to their evident differences in physical surroundings ; 
but it will be seen that this expectation has not been fully borne 
out. Most of the common species of Cladocera and Copepoda 
are generally distributed all over the district, and appear to be 
indifferent even to extreme differences of salinity and botanical or 
physical surroundings. Still there are certain species whose range 
is definitely restricted, and I have dealt with most of these at some 
length in the preceding list. The only factor influencing distribu- 
tion which at present can be determined is the salinity of the 
water, and I believe it to be a factor of great importance. 
I propose now to take the Broads mentioned in the table and to 
show that they fall more or less into groups characterised by 
certain zoological, or other features. 
One group' of Broads stands out from the rest as peculiarly 
distinct. This group includes Hickling, Horsey Mere, Martham, 
and Heigham Sounds ; in other words all the Broads connected 
with the Thurne above Potter Heigham. I propose to call this 
the Hickling group. In all these Broads the salinity of the water 
is very high. In part this high salinity is no doubt due to their 
proximity to the sea — Horsey Mere, for instance, being only 1| 
miles from the coast ; but it is quite impossible to explain the 
whole of the saltness in this way. As a matter of fact, it can be 
shown that the source of the salt lies in the Broads themselves, 
* I have included in this table a few records for which I am indebted to 
Mr. Scourfield. These records are not all included in the body of the paper. 
