294 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA. 
of March with May, June, and so on. It was, therefore, 
necessary to compare each month with every other month, 
and then to take the means of the results thus obtained and 
the result is shown in the plain line curves in Chart I, which 
do not quite agree with the dotted curves. 
I have thus obtained a new set of curves for 1904, which 
must supersede the curves shown in table 1, p. 64, of my 
previous paper. 
During the past season I have worked over the same col- 
lecting area as in 1904, visiting for the most part the same 
collecting stations regularly from March to October, except 
in July, when I was away in Scotland. During the 7 months 
I have made 715 collections, the number being smaller than 
it would have been had not August been such a bad month 
as already mentioned. 
On the method referred to I have worked out the curves 
of species per collection of the Hydradephaga and Palpicornia 
for 1905, and they are shown in Chart 2, side by side with 
the new 1904 curves. I have also inserted in the 1904 chart 
a curve the result of working out the collections omitting 
July, in order to be able to make a fair comparison between 
the seasons 1904 and 1905. 
Now there are, of course, no data in the curves for 1904 and 5 
which admit of their being compared for relative abundance ; 
that is, there is nothing to show whether the June maximum 
of 1905 is greater or less than the September maximum of 
1904. In order therefore to trace the relative numbers of 
species per collection during the two seasons, I have compared 
similar months in the two years — on the principle already 
referred to, using only collections common to each pair of 
months — and from such a comparison we can tell whether 
in March, 1904, individuals were more or less widely distributed 
than in March, 1905, and similarly for other months, and the 
results are set out in Chart 3. 
From this chart it will be seen that except in March, Sep- 
tember and October, the 1905 collections were richer in 
Hydradephaga than the 1904 collections, and that in 
Palpicornia were richer during the whole season with the 
