72 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA 
Now it must be clearly understood before considering 
these percentages that the results are only indicative and are 
not to be taken as statements of fact. In such a comparison 
as I have made, where the conditions at each station are 
unequal, and where unequal numbers of collections have 
been made at each station, and where all sorts of unknown 
factors interfere, correct results are almost if not quite 
impossible ; but I think if we use the results obtained only 
as an indication of probabilities they may prove useful as 
a guide for further investigations. 
From a table such as this we can extract several things. 
In the first place the richness of each of the sub-districts in 
species, which is as follows : — 
TABLE 4. SHOWING NUMBER OF SPECIES OCCURRING 
IN EACH DISTRICT. 
Name of District 
Ant. 
Hicki.ing. 
Palling. 
Coast. 
Ormesby. 
Muck 
Fleet. 
ea 
pc 
No. of Collections 
in each district. 
236 
179 
217 
S 7 
67 
70 
119 
Total Number 
of Species 
in all districts, 
■15 
92 
9 i 
96 
72 
76 
61 
So 
This result must, however, be taken with some caution, 
as the comparison is not quite fair, seeing that the Ormesby 
district had only 6 7 chances of showing its species while the 
Ant district had 236. That Palling district produced most 
species may perhaps be accounted for by the variety of its 
stations. 
Secondly, it is possible to extract the average number of 
species per collection in each sub-district and the result is 
as follows 
