IN THE NORFOLK BROADS DISTRICT. 69 
the latter half of September, thus corresponding with the 
hatching times of the groups. 
Now having endeavoured to indicate the process of 
distribution, I will turn to the consideration of the localisation 
of species within the district. In the first place of course the 
usual place to look for Water Beetles is in water, so a first 
step in localisation is simple. But it is not every piece of 
water that produces every species of Water Beetle, so that 
it is necessary to take some steps to discover the principles, 
if any, upon which further localisation depends. 
With the object, therefore, of seeing whether one part of 
the Broads District is more suitable to some species than 
another part, I have grouped the various collecting places 
into stations, and the stations into sub-districts, each sub- 
district being composed of a group of stations situated nearer 
to one another than to those of other sub-districts, as will be 
seen from the accompanying map. 
There are seven such sub-districts ; as will be seen, their 
arrangement coincides fairly well with the physical character- 
istics of the locality. We have, for instance, the Ant and the 
Bure districts situated in the respective river valleys ; the 
Muck-Fleet district just within reach of the salt tides which 
occasionally run up the river ; the coast district, exposed to 
the easterly and north-easterly gales which bring in sand and 
salt spray, and the Hickling district continuous with the 
coast marshes, but somewhat protected from the sea winds 
by belts of trees ; the Palling district, partaking of the nature 
of the Hickling and the coast districts, stations 10 and 19 
being somewhat sheltered, while 11 and 12. although not so 
close to the sea as some of the coast stations, are exposed to 
the east ; and lastly, the single Ormesby station, well protected 
on all sides by woods but within easy reach of the coast. 
In these 7 sub-districts 975 collections have been made at 
the 27 stations, and 115 species of Water Beetles have been 
found. I have worked out from this material the percentage 
of occurrences of each species in each sub-district with a view 
to comparing one sub-district with another, and the result 
is seen in the following table. 
