38 



Many of them have one or more fine lines across the underside of the wings, 

 whence arises the name "Hair streaks." A curious characteristic of the 

 genus is, that the members of one sex often have a satin or plush-like patch 

 on the fore-wings, at the extremity of the discoidal cell. The caterpillars 

 appear to frequent trees and shrubs instead of herbaceous plants, as is the 

 custom with those of the allied genera ; and the perfect insects are enabled, 

 by their robust structure, to fly with great power over the -branches of even 

 the highest oaks and other forest trees. 



Writers have divided this genus into two or three sub-genera. Dalman 

 separated those species in which the males have a velvety patch on the fore- 

 wings, under the name Zephyrw. This arrangement is followed by Kirb), 

 in his " Catalogue of Diurnal Lepidoptera." Hubner, however, had made 

 the same division at an earlier date, and had still further divided the group. 

 These in which the males had a velvety patch on the fore-wings, he called 

 Bithys ; those without a patch, Strymon ; and the tail-less species he called 

 Lyons. To those who study British insects only, this sub-division may 

 appear unnecessary, but the advantage is very apparent when we consider 

 the large number of species. Each sub-genus has its British representative, 

 as will be seen. 



SUB-GENUS BITHYS, Hubner. 



ZEPHYRUS, Dalman. 



[Females with a more or less velvety patch on the fore-wings. 

 ZEPHYRUS is a bad generic name, being the specific name of one of the 

 Polyommati. 



THECLA BETUL.E. 



Brown Hair-streak. 



BETUL^E, Linn. Bet'ulse, from the generic name of one of its food-plants 

 the birch, Betula alba. 



This is the largest species of the genus found in Europe, measuring some- 

 times an inch and two-thirds in expanse. The sexes differ considerably on 

 the upper side, the male being of a deep brown colour, slightly paler near the 

 centre of the fore-wings, whilst the female possesses on the front wings a 

 a large patch of clear orange. Both sexes have several orange marks upon 

 the lower angles of the hind-wings. On the underside the general colour is 

 a tawny orange with duller bauds, and marked with one white line on the 

 fore-wings and two parallel white lines on the hind-wings. 



This butterfly is later on the wing than any other species of the genus. 

 The earliest specimens emerge in the end of July, and they continue to appear 

 for some time, remaining out till September or even October. 



