Mr. Fereday has described and figured a very interesting variation occurring in the structure of the costal veins of this species,[54] vein 11 of the fore-wings sometimes running into 12 (see Plate I., fig. 26), and sometimes being entirely absent (fig. 25). After reading Mr. Fereday's article I examined the specimens in my own collection, and found that all those taken on Mount Arthur and on Mount Peel, in the Nelson district, had veins 11 and 12 joined, whilst the two specimens I took on Mount Enys, Castle Hill, West Coast Road, had vein 11 absent. As, however, Mr. Fereday has specimens exhibiting both forms of neuration, from Castle Hill and from Mount Hutt, I do not think it likely that the peculiarity is confined to butterflies from any particular locality. Like Mr. Fereday, I have observed that the specimens having veins 11 and 12 joined, are smaller than those having vein 11 absent.
The perfect insect appears in January, February and March. It frequents shingle slopes on mountains, at elevations ranging from 4,000 to 6,000 feet above the sea-level. Sometimes the butterflies occur in considerable numbers, flying in a lazy, aimless manner in the scorching sunshine, but instantly retreating into crevices between the stones when the sun is obscured. I have observed that this species is most abundant in the neighbourhood of the carpet grass, on which I fully anticipate its larva feeds. It seldom, however, settles on this grass, preferring to alight on the shingle, which, owing to the rarefied air existing at such high elevations, soon becomes intensely heated by the sun's rays.
When disturbed this insect flies with considerable rapidity and thus often eludes the net, so that the capture of a good series of specimens on a rugged mountain-top is usually very exciting, if not actually dangerous work. As with many other { 115}insects, mountain ranges are more prolific in this butterfly than isolated peaks. Mount Peel, situated to the west of Mount Arthur, is the best locality I know of for this and many other Alpine species. Its gentle slopes enable the collector to work with perfect ease and safety, whilst the patches of rich soil occurring nearly to the top of the mountain support an unusually varied Alpine flora of great interest.