VERTICAL DISTRIBUTIOiST OF BRITISH LEPIDOPTERA. 39 



The Grampian Mountains, in latitude 57° (wliich possess a 

 mean annual temperature of 47° F. at the sea-level), may be 

 taken as the standard for the British Isles, and in estimating 

 their equivalent zones in other parts of the country an allowance 

 of 300 feet for every degree of mean annual temperature has 

 merely to be made, either added or deducted, as the case may 

 be, whether it represents a higher or a lower figure respectively. 

 This is founded on the well-known principle that for every 300 

 feet, or thereabouts, Avhich one ascends up a mountain, the tem- 

 perature falls about 1° F. The accompanying table will, I think, 

 make this matter perfectly clear. 



The best method undoubtedly for the entomologist to calculate 

 the height of the various altitudes to which he ascends, is by 

 means of an Aneroid barometer, wbich can be carried very easily, 

 as it is only a small instrument. The cost of a good one, marked 

 up to about eight or ten thousand feet, would be about £5. Other 

 methods may be adopted, but this one is the best, I think, for our 

 purpose. In recording observations upon the Lepidoptera occur- 

 ring in each vertical belt or zone, the student should draw a 

 distinction between those species which permanently reside 

 within the limits of each and those which only visit them 

 occasionally. A few examples will make this better understood. 



Vanessa cardui has been seen upon the summit of Snowdon 

 (3570 feet above the sea-level), while Vanessa urticce and Ar(ji/nnis 

 aglaia have both been observed on the top of Cader Idris (2930 

 feet in altitude) ; but it stands to sense that none of them were 

 bred at anywhere near to elevations named, as their pabula do 

 not grow at anything like the height upon any mountains in this 

 country. On the other hand, the following species possess such 

 a weak power of flight that it would be quite safe to say that they 

 had undergone their metamori)lioses in the neighbourhood at 

 wliich they were found. I allude to Erehia epipliron var. cassiope, 

 which occurs on the mountains of Cumberland at the height of 

 1500 feet ; Erehia cetliiops, which is found in the region of the 

 Grampians, from the sea-level to the height of 800 feet ; and 

 Coinonympha typlion, which occurs in the same range, at no less 

 an altitude than 2000 feet. 



The student should also take special note of the number of 

 broods found in each zone (those having two flights in the lower 

 ones generally possessing only one at higher elevations) ; also of 

 the varieties of each species in each zone of those which are 

 common to two or more of them, many species in the higher 

 zones developing either meianic or melanochroic tendencies when 

 compared with their types in lower or more southern localities. 



The study of the vertical distribution of the British Lepi- 

 doptera as here mapped out cannot, I think, fail to prove a new 

 and very interesting source of pleasure to many nn entomologist 

 who wishes to direct his energies though some additional channel. 



