8 INSECTA MADERENSIA. 



on the legs. I liave hitherto observed it in no islands of the group except Madeii'a 

 proper, and only there at high elevations, — where however it is extremely abun- 

 dant. It occurs in the greatest profusion, from the end of the summer to the 

 early spring months, beneath stones, in the lofty mountain district between the 

 Pico da Lagoa and the Pico dos Ai-icros ; as also on the flat alpine plain of the 

 Paul da Serra, from 5000 to 6000 feet above the sea. Although so common 

 throughout Eiirope, it is perhaps, when geographically considered, one of the most 

 interesting of the Madciran Coleoptera, as affording another and even more 

 striking example, not only of the modification of form in a normally northern insect 

 when on its southern limit (the result, however, perhaps more strictly, as in the 

 case of the varieties of the D. sigma, of isolation rather than of latitude) ; but as 

 showing, likewise, how a species abundant on the low sandy shores and sheltered 

 sea-cliffs of more temperate regions finds its position here only on the summits 

 of the loftiest mountains. It is true that the aberration from the tj'pical state, as 

 in the D. sigma, is not in the present instance very considerable ; yet, when the 

 cii'cumstances producLng it are taken into account, I am persuaded that the 

 difference is exactly of that nature on which too great stress cannot possibly be 

 placed, when discussing the general question of geographical distribution as having 

 a tendency, more or less directly, to affect both colour and form. It is well kno^^-n 

 to naturalists that a multitude of insects from the New "World, receding from then- 

 Em-opean analogues merely in certain excessively minute characters, have usually 

 Ijeen pronounced at once as new to science, first because those differences are con- 

 stant, and secondly because the specimens have been received from the other side 

 of the Atlantic. And yet in instances like the present, as in many others which 

 Ave shall have occasion to notice, — in an island which, while it belongs artificially 

 to Europe, is yet, natm'ally, sufficiently distinct from it as to form at any rate a 

 step])ing-stone to the coast of Afi-ica and the mountains of Barbary, — species 

 similarly cu'cumstanced are not necessarily received as new (and rightly so, I ap- 

 prehend), though in every respect affording differences not ovlj analogous to those 

 already mentioned, but in many cases positively identical with them. If however 

 a specific line of demarcation does of necessity exist between the creatures of the 

 Old and New AVorlds, the problem yet remains unsolved, so long as intermediate 

 islands present parallel modifications, where that line is to be di-a-sAii. Meanwhile, 

 how far geographical varieties of this kind, concerning the non-specific claims of 

 wliich confessedly but little doubt can exist, may lead to the explanation of the 

 Transatlantic ones just referred to, I will not venture to suggest. Yet certain it is 

 that tlic one case bears directly on the other; and that, if we can prove that 

 common European insects when isolated in the ocean become in nearly all cases 

 more or less modified externally in form, there is at least presumptive evidence 

 that the law Avill hold good on a wider scale, and may be extended not only to the 

 Atlantic itself, but even to cotmtries beyond it. The differences of the present 

 Dromins from its more nortlicrn representatives arc, as just stated, small ; never- 



