on that rock, "that, had the case been a solitary one, I should not have hesitated in regarding the specimens obtained from thence as specifically distinct; nevertheless, with the knowledge both of the modifying effects of isolation, and also of the _kind_ of modification essentially peculiar to that island, I am perfectly satisfied that it is a mere local state, although a very remarkable one, and has no claim whatsoever to be otherwise considered[41]." The _Pecteropus Maderensis_, Woll., is of a greenish-brassy tinge in Porto Santo, and much acuminated in front; whereas on the Dezerta Grande it is almost invariably _coppery_, and less narrowed anteriorly. The _Caulotrupis lucifugus_, Woll., although ranging through no very opposite phases, either of outline or sculpture, "appears to possess a slight modification for every island of the Madeiran Group: and hence small shades of difference, which might otherwise be regarded as trifling, become directly important, and cannot be ignored in a local fauna,--even though a general collector may deem it unnecessary to recognize them. In real fact, however, such distinctions, when viewed geographically, are of the greatest interest, as serving to illustrate what we have so often had occasion to comment upon, namely the influence of isolation and other circumstances on external insect form[42]." The _Psylliodes vehemens_, Woll., is permanently paler in Porto Santo than it is in Madeira proper, being almost entirely testaceous. "That the species is identical, however, with the Madeiran one I have not the slightest doubt,--the sculpture and colour, as I conceive, having merely undergone a change since the remote period of its isolation on a comparatively calcareous soil[43]." The _Scarites abbreviatus_, Koll., occupies the loftiest peaks of nearly all the Madeiran islands, and was probably once abundant over the entire ancient continent, whatsoever its limits may have been, of which the present group forms but an isolated part. "There are traces of it in the Canaries, from whence occasional specimens have been brought, and which, from the want of local data and of sufficient numbers to reason upon, have in their turn been severally regarded as distinct. The fact however is, that the species in question is an extremely variable one, assuming differences of size according to the altitude at which it lives, and differences of sculpture according to the circumstances of the spot on which it is isolated. That such is actually the case, a careful observation of the many minute changes which the insect has undergone in the various islands and altitudes of the Madeiran group will, I think, prove to a demonstration. For it is impossible to suppose that every rock contains its own _species_, that is to say, has had a separate creation expressly for itself,--a conclusion at which we must assuredly arrive, if small and even constant differences are _of necessity_ specific. Rejecting therefore