134 Browne: The Aquatic Coleoptera of the Isle of Man. 
labelled “K, 2; vii., 1908,’ the’ ""K” YW belteves standine tor 
“ Kentraugh.’ te 
With regard to systematic arrangement, there are two 
points upon which I have been unable to follow recent writers. 
After’ examining large ‘numbers of Haliplus ruficollis, | have 
been’ unable to satisfy myself as to the specific distinction 
between it and H. immaculatus, a specimen of which I received 
from Mr. E. A. Newbery. Shape alone is, at the best, a poor 
criterion upon which to seperate species, and the shape of the 
group at present included under the name rzjicollis varies so 
much that I can find no break which should justify the separa- 
tion from it of H. wmmaculatus. Perhaps an investigation of 
the whole ‘ ruficollis’ group would clear up the difficulty by 
discovering some distinct specific characters, and perhaps 
several species! 
Edwards* recently re-separated Anacena ovata and limbata 
as distinct species, and I have not followed him in this. Edwards 
admits that these two forms and A. bipustulata are ‘ evidently 
very closely allied.’ I will not enter into the question of the 
specific distinction of the latter, as it does not occur in the Isle 
of Man, and I have not worked at it, but so far as my experience 
goes, it 1s easily separated, and has a distribution limited to 
the south-east of England (Lincs. N., to Hants S.), except for 
a single record for Lancs. S. 
The other two forms are not easily separated, as I find all 
intermediate grades of colour between the black (limbata) and 
the brown (ovata) and both forms seem to be widely distributed 
in the country, the black one apparently being the rarer. 
Out of seventy collections made during the past season (Ig10), 
the black one occurred twenty times, and the various browns 
fifty-eight times, so that in only eight collections did black 
and brown occur together. I think the colour is affected by 
the environment, the black specimens occurring chiefly in a 
kind of peaty water, which is not too acid for certain snails, 
such as Planorbis spirorbis, and where the water beetle fauna 
includes helophil and oxylophil species, e.g., H. gyllenhalit, 
vittula and nigrita, I.obscurus, Ph. melanocephalus, etc. There 
are several other species of water beetles with colour varia- 
tions as for instance, Deronectes depressus and 12-pustulatus, 
Platambus maculatus, etc., and I think the differences between 
their extreme forms, the strongly yellow marked and the black, 
are quite as great as in the case of the Anacenas. In the case 
of these species, the dark form of P. maculatus is commoner 
in the north than in the south, and on high than on low grounds, 
while I think that the dark forms of the two Deronectes, 
* “On the British Species of Anzcena,’ E.M.M., Ser. 2, xx., 1900, pp- 
169-171. 
Naturalist 
