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XXI. The water-beetles of Jwpan. By David Sharp. 

 [Bead September 3rd, 1884.] 



In the * Transactions ' of this Society for 1873 will be 

 found a paper on this subject, and a supplement thereto 

 was published in the volume for the ensuing year, 1874. 

 The present paper, together with the two just alluded to, 

 will be found to enumerate all the water-beetles of the 

 families Hali2}lidcs, Dytiscidce, Gyrinidce, and Hydro- 

 philida at present detected in the Japanese islands. 



Mr, Lewis' recent visit to Japan has demonstrated 

 that the coleopterous fauna of those sunny islands is 

 richer comparatively than the corresponding regions of 

 Europe ; but the water-beetles form apparently an 

 excejjtion to this rule, and the fauna in this department is 

 in variety and number of species at present inferior to that 

 of our own part of the globe. It is probable, however, 

 that this is to a certain extent due to the fact that water- 

 beetles require special modes of collecting, and are thus 

 apt to be neglected, and also to the fact that they are 

 comparatively more numerous, or at any rate more 

 accessible in northern lands : as an instance of which it 

 may be mentioned that Lapland is very rich in these 

 insects. The fauna of the northern portions of the 

 Japanese Archipelago is as yet not so well known to us 

 as that of the southern parts, and, when it has been 

 well explored during favourable seasons, it will probably 

 be seen that the poverty of Japan in water-beetles is 

 not so great as it at present appears. 



A detailed comparison of the water-beetle fauna of 

 Japan with that of other regions would therefore be at 

 present premature ; but I can scarcely omit to point to 

 the fact that as yet but one species of the great genus 

 Hydroporus has been detected there, while in Britain 

 it is represented by thirty-six species ; and North 

 America is also very rich in it. 



The total number of Dytiscidce known from Japan is 

 at present only about forty species, while in Britain we 

 have 105. 



TRANS. ENT. SOC. LOND. 1884. — PART IV. (dEC.) 2 H 



