II.— ON AQUATIC CARNIVOKOUS COLEOPTERA OR DYTISCID.E. Br 

 David Sharp, m.b., Hox. Mem. of the Institute of New Zealand: Member of 

 THE Entomological Societies of London, France, Berlin, Stettin, Belgidm 

 and Switzerland, &c., &c. Plates VII to XVI fl. 



[Read May 16tli, 1881.] 



1. Prefatory. 



Some years ago. I commenced a special study of the Dytiscidoe, 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 tbe 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 DytiscidjE — 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 knc'Wii onlv 

 by a single, or by very few individuals, and thus the basis of their taxonomy — ti <• 

 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 eaith'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 



TSlAKS. rot. dub. 80C. N.S., VOL. II. 2 B 



