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Show 336 ISLAND LIFE. numbers are, generally speaking, proportionate to th~ richness of the district and the amount of work bestowed upon 1t; Scotland, however, giving more than its due proportion in this respect, which must be imputed to its really possessing a greater amount of speciality. The single peculiar Irish species stands as a monument of our comparative ignorance of the entomology of the sister isle. The peculiar species of Apion in the Shetland Islands is interesting, and may be connected with the very peculiar climatal conditions there prevailing, which have led in some cases to a change of habits, so that a species of weevil ( OtioThynchus rnaurus) always found on mountain sides in Scotland here occurs on the sea-shore. Still more curious is the occurrence of two distinct forms (a species and a well-marked variety) on the small granitic Lundy Island in the Bristol Channel. This island is about three miles long and twelve from the coast of Devonshire, consisting mainly of granite with a little of the Devonian formation, and the presence here of peculiar insects can only be due to isolation with special conditions, and immunity from enemies or competing forms. When we consider the similar islands off the coasts of Scotland and Ireland, with the Isle of Man and the Scilly Islands, none of which have been yet thoroughly explored for beetles, it is probable that many similar examples of peculiar isolated forms remain to be discovered. Mr. Rye hardly thinks it possible that the Dromius vectensis can really be peculiar to the Isle of Wight, although it is abundant there, and has never been found elsewhere; but the case of Lundy Island renders it less improbable; and when we consider that the Arum italicum, Galamintha sylvatica, and perhaps one or two other plants are found nowhere else in the British Isles, we must admit that the same causes which have acted to restrict the range of a plant may have had a similar effect with a beetle. I must also notice the Gatho'rmiocerus maritimus, because its only near ally inhabits the coasts of the Mediterranean; and it thus offers an analogous case to the small moth, Elachista rufocinerea, which is found only in Britain and the extreme South of Europe. Looking, then, at what seem to me the probabilities of the case from the standpoint of evolution and natural CHAP. XVI.) THE BRITISH ISLES. 837 selection, and giving due weight to the facts of local distribution as they are actually presented to us, I am forced to differ from the opinion held by our best entomological authorities, and to believe that some considerable proportion of the species which, in the present state of our knowledge, appear to be peculiar to our islands, are, not only apparently, but really, so peculiar. I am indebted to Mr. Robert McLachlan for the following information on certain Trichopterous N europtera (or caddis-flies) which appear to be confined to our islands. The peculiar aquatic habits of the larvre of these insects, some living in ponds or rivers, others in lakes, and others again only in clear mountain streams, render it not improbable that some of them should have became isolated and preserved in the mountain districts of our western coasts, or that they should be modified owing to such isolation. In these insects the characters depended on to separate the species are wholly, structural, and the care with which Mr. McLachlan has studied them renders it certain that the species here referred to are not mere varieties of known continental forms, however closely they may resemble them in form and coloration. l'1·ichoptem peculiar to the British Isles. 1. SETODES ARGENTIPUNCTELLA.-This spe<:ies is known only from the Lakes Windermere and Killarney. It has recently been described by Mr. McLachlan, and is quite distinct fTom any known species though allied to S. punctata and S. vi1'idis, which inhabit France and Western Europe. 2. RHYACOPHILA MUNDA.-Described by Mr. McLachlan in 1863. A very distinct species, found only in mountain streams in Wales and DeYonshire. 3. PHILOPOTAMUS INSULARIS. (? A variety of P. montanus.)-This can hardly be termed a British species or variety, because, so far as at present known, it is peculiar to the island of Guernsey. It agrees structurally with P. rnontanus, a species found both in Britain and on the continent, but it differs in its strikingly yellow colour, and less pronounced markings. All the specimens from Guernsey are alike, and resident entomologists assured Mr. McLachlan that no other kind is known. Strange to say, some examples from Jersey differ considerably, resembling the common European and British form. Even should this peculiar variety be at some future time found on the continent it would still be a remarkable fact that the form of insect inhabiting two small islands only twenty miles apart should constantly differ ; but as Jersey is between Guernsey and the coast, it seems just possible that the more insular conditions, and perhaps some z |