( 439 ) 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
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