302 Mr. A. R. Wallace on 



and-twenty genera, combined with the form of the antennae, palpi 

 and anal valves, all of which vary perhaps more than is usual. 

 The form and texture of the wings also seem very subject to 

 modification within certain limits, as is well seen by comparing 

 the delicate elongate forms of Lcptalls and Leucoi^hasia with the 

 strong and compact Call'idryas and Colias ; and in colouration no 

 contrast can be greater than that between such genera as Euterpe 

 and Gonepteryx, Perhaps too there is no family more generally 

 and uniformly distributed over the whole earth. Pieridce inhabit 

 the deserts of Arabia as well as the tropical forests; they sport 

 about the snows of the Himalayas and roam over the icy plains 

 of Siberia. The variety of conditions to which they are subject 

 is therefore as great as can well be conceived, and the considerable 

 generic diversity that exists among them probably indicates a 

 great antiquity for the group, yet the ever fluctuating characters 

 of colour, form and marking have nevertheless their strict limits 

 which they in no case overpass. 



The large amount of diversity in the neuration of the wings 

 of the Pler'ulw, together with the considerable differences in the 

 form of the antennae and palpi, have led to the establishment of a 

 number of well-marked generic groups. In the " Genera of 

 Diurnal Lepidoptera," published about the year 1847, Mr. Double- 

 day admitted sixteen genera of Pier'idcB. Since that time five 

 have been added, most of which were indicated and even named 

 by him as distinct sections of genera. In the present paper I add 

 two, formed out of the old genus Pieris, thus raising the total 

 number of genera to twenty-three. These are distributed with 

 tolerable equality through the great zoological divisions of the 

 earth ; the South American and Australian regions each having 

 eleven, the African region ten, the varied Indian region (in- 

 cluding the western Malay Islands) fifteen, while the Nearctic 

 aud Palaearctic regions each possess six genera. 



The extreme isolation of the South American continent from 

 the other tropical regions is indicated by its possessing three 

 peculiar genera, — Euterpe, Leptalls and Hesperocharis, — while the 

 Indian region has but two, Prioneris and Dercas, and the 

 Australian and Palaearctic but one each, Elodlna and Leucophasia 

 respectively. The Nearctic and the Ethiopian regions have no 

 peculiar genera. Only a single genus is universally distributed 

 over the globe, the true Pieris. This has representatives both in 

 the polar and the equatoreal regions, on the highest mountains 

 and over the hottest plains. Callidryas, Terias and Tachyris 

 are tropical groups which range round the equatoreal regions of 



