158 THE NEUltOPTEHA OF GUERNSEY. 



ascertain whether it occurs in the neighbouring island of 

 Jersey, or on the opposite coast of France. 



" In general form and structure this so precisely agrees 

 with Montanus that I fail to find any differences, but its 

 peculiar colour and markings are so constant as to fully 

 entitle it to rank as distinct. 



" It may be that we have here a well-marked instance of 

 the power of long isolation to produce a form worthy of being 

 considered specifically distinct." 



In Supplement, Part 2, page 71, of the same work, Mr. 

 McLachlan remarks : — " I have succeeded in obtaining a 

 Philopotamus from Jersey, for purposes of comparison with 

 the distinct form from Guernsey that I named Ph. insularis 

 (page 384). Mr. W. A. Luff made an excursion to Jersey, and 

 found a species at a stream near Plemont Point in that island. 

 I can only regard these as montanus. They have the golden 

 yellow of the anterior wings more extended than is usual 

 in continental examples, but not more so than is often the 

 case in others from Britain ; and they do not show an approach 

 towards the Guernsey insularis, which thus maintains its 

 insular distinctness." * 



I also quote the following extract from " Wallace's Island 

 Life," under the heading " Tnchoptera peculiar to the British 

 Isles":— 



" 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. montanus, 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 

 peculiarity of the soil and water in the former island have 

 really led to the production or preservation of a well-marked 

 variety of insect." 



* P. Insularis has recently been recorded from Sark (see The Entomologist's 

 Monthly Magazine, March, 1892, page 74). 



