THE ATHALIA GROUP OF THE GENUS MELITJEA. 303 



difference than is usually caused by altitude in other species. 

 What has been said of altitude is also true, in a general way, of 

 latitude, but in both cases there are various further points to be 

 taken into consideration, such as the suitability of the environ- 

 ment to the food-plant, the length of time which the snow 

 generally remains, the amount of possible daily sunshine, the 

 chilling effect of the near neighbourhood of glacier-torrents, &c. 

 It is possibly in connection with the first of these considerations 

 that athalia, in the neighbourhood of the Italian Lakes, is smaller 

 than the usual mountain form, those from Cadenabbia, for in- 

 stance, being smaller than specimens from Faido far up the 

 Leventina. It seems hardly possible that my specimens from 

 the former locality, taken towards the end of July and not very 

 fresh, could belong to a second brood ; and, indeed, Riihl has 

 remarked on the smallness of the Tessin and Lombardy speci- 

 mens as compared with those from further north. With very 

 few exceptions it is useless to give definite rules for the times of 

 appearance of the different species, in consequence of the great 

 extent of the habitat of many of them both in altitude and 

 latitude. Such rules as can be laid down must be vague and 

 comparative. It may, however, be said that asteria and raria 

 never descend low, probably not below 6000 ft. at most, while 

 hritomartis and deione never mount high, nor does the latter go 

 far north, the Rhone Valley being quite its limit. Asteria is to 

 be found from the beginning of July till at least the middle of 

 August, and varia from the middle of July for about a month. 

 Parthcnie emerges before athalia, and in the plains is generally 

 over when the latter appears, but the higher or the further north 

 one goes, the more they may be expected to overlap, though, in 

 my experience, parthenie is always the earlier, even where it is 

 single-brooded. In the Rhone Valley it may be expected about 

 the middle of May, and again about the middle of August. In 

 the same district aurelia appears a few days later, berisalensis 

 and dictynna at the beginning, and athalia in the middle of June, 

 the first-named appearing again about the third week in August 

 or a little later. Britomartis at Reazzino appears fairly early in 

 June and at the end of July. From these dates it can be more 

 or less calculated at what time the emergence of a species may 

 be expected as we rise higher or advance further north, though, 

 as previously stated, many local circumstances, as well as the 

 forwardness or otherwise of the season, must be considered. It 

 may also be added that, with the exception that deione appears 

 in South France in May, none of the species can be expected to 

 appear further south much earlier than their Rhone Valley 

 dates ; altitude has, moreover, in general a more retarding effect 

 than latitude. 



