DISTRIBUTION OF THE BRITISH BUTTERFLIES. 269 



Palcemon, are found beyond or on the arctic circle ; while five others 

 occur above or near the 60th parallel of north latitude, namely, 

 Polycliloros (which has occurred in Scotland, though perhaps it 

 can scarcely be considered a true native), Cinxia, Adii:)pe, Arion, 

 and Palismon ; and four more, namely, DapUdice, Bellargus, Pruni 

 and W-albu7n have been detected in Scandinavia. We thus have 

 thirteen species which inhabit latitudes north of the British 

 Islands, and which, therefore, so far as that goes, ought to occur 

 in Scotland and Ireland. Of the remaining six species, Dispar 

 may be put aside as a species the typical form of which was 

 confined to England, and is now unhappily extinct. For the 

 remaining five — Sibylla, Iris, Galathea, Cory don and Actceon — the 

 latitude of Scotland and Ireland is rather beyond the range 

 of the species. 



Let us now return to the thirteen species which range north 

 of Britain, and find, if possible, a reason for their absence. For 

 most of them the reason is, I think, the insular nature of the 

 climate. By an "insular" climate is meant one which by the 

 proximity to the ocean has a greater humidity and less extremes 

 of heat and cold than is the case when the ocean is more distant, 

 or its influences obstructed by intervening high land. That an 

 insular climate affects very considerably the range of plants has 

 now been proved, and it is but natural to suppose that similar 

 influences may afl"ect insects. Of the thirteen English species 

 whose absence from Scotland and Ireland we are now considering, 

 several, if not all, occur in those parts of England which have a 

 more "continental" climate. Of these Machaon, DapUdice^ 

 Cinxia,* Arion, Palcemon, Comma, are good examples. But in 

 addition to these climatic reasons there is the unexplained 

 tendency of some species to be local and rare, especially on the 

 confines of the regions that they inhabit, and which must not be 

 altogether lost sight of in discussing geographical distribution. 



Let us next consider the species, nine in number, which 

 inhabit Ireland, and are not to be found in Scotland. Of these, 

 six — Sinapis, Rhamni, C-alhiim, Athalia, Lathonia and Argiolus — 

 occur in latitudes north of Scotland (two of them, AtJialia and 

 Lathonia being indeed arctic), two are Scandinavian [Betidce and 

 Thaumas), and the remaining one, Hyale, has been possibly seen 



* It must not be supposed that because the Isle of Wight is an island that its 

 climate is thereby "insular." 



