IIl.—ON AQUATIC CARNIVOROUS COLEOPTERA OR DYTISCIDA. By 
Davip SHarp, M.B., Hon. Mem. or tae Institute or New Zeauanp: MrmpBer or 
THE ENTOMOLOGICAL SocreTies or Lonpon, France, Beruin, Srerrix, Bereium 
AND SWITZERLAND, &c., &c. Prates VII tro XVIII. 
[Read May 16th, 1881. ] 
1. PREFATORY. 
Some years ago [ commenced a special study of the Dytiscide, with the object 
of increasing the recorded information about this family of beetles. I had been 
previously, for a considerable period, specially interested in the family, and when 
beginning my studies, I hoped particularly that I should be able to improve the 
very imperfect classification in vogue, and I also wished to know whether a detailed 
knowledge of the varied structural peculiarities of the species would be consistent 
with the belief that the present condition of these had been reached by a process 
of gradual modification or evolution, and whether an intimate acquaintance with 
the intricate relations existing between the diverse components of the family would 
render credible the hypothesis that these are descended from a few ancestors or even 
from a single very remote ancestor. 
Now that I am offering to the Royal Dublin Society the work that has occupied 
me for some years, I feel that I must in the first place make an apology for its 
imperfections and omissions. I have accomplished but little—so little that, in 
comparison with what I have left undone, I feel it to be almost as nothing. Our 
knowledge of the earlier stages of the life of Coleoptera, and of their meta- 
morphoses is very imperfect, and in the case of the aquatic species there are special 
difficulties in the way of acquiring information of this nature, thus it happens that 
we know very little of the life histories of the Dytiscidze—so little that it cannot 
aid at present in the classification of these insects, and I have therefore limited my 
efforts to producing an arrangement based on the structures of the perfect insect. 
Even as thus limited the work is very incomplete ; existing collections though 
tolerably numerous are very imperfect ; a large number of species are known only 
by a single, or by very few individuals, and thus the basis of their taxonomy—the 
accurate delineation of the characters of morphological species—is still very in- 
complete, while the important questions of the amount of variation exhibited by 
the different forms, and of the limits and nature of their distribution on the earth's 
surface can be dealt with only in a very inadequate manner. 
Moreover, I have made no reference to internal anatomy, for in view of the 
present position of this department of entomology it is clearly premature to attempt 
to make a classification founded on both the internal and external structures ; and 
TRANS. ROY. DUB. SOC. N.S., VOL. IL 2B 
