155 



THE GEOGRAPHICAL DISTRIBUTION OF THE 

 MOTHS OF THE SUBFAMILY BISTONINAE. 



J. W. HESLOP HARRISON. D.Sc. 



XVII.— THE GENERA NACOPHORA (HULST), 

 PH.EOURA (HULST), AND THYRINTEINA (MOSCHL). 



Nacophora quernaria (Abbot and Smith). Distribution : — 

 The Atlantic States. 



Nacophora phigaliaria (Guen). Atlantic States. 



Nacophora ypsilon (Forbes). Atlantic States. 



Nacophora cupidaria (Grote). Florida. 



Nacophora minima (Hulst). Colorado. 



PhcBoura mexicanaria (Grote). Mexico. 



Thyrinteina arnohia (Cramer). Intertropical North, Central 

 and South America. 



Nacophora and its immediate allies, whilst undeniably 

 Bistonine in all essentials, nevertheless carry what ma}- be 

 regarded as a distinctively Boarmiine structure in the fovea — 

 a peculiar depression on the underside of the forewings which 

 is very likely an alluring gland for sexual purposes. In it 

 can be perceived a token bespeaking the fons ct origo of the 

 true Boarmiince, known from their wide distribution to be an 

 enterprising assemblage of extreme age, for there is not a 

 hole or corner of the whole globe to which it has not penetrated. 

 Whilst many of the Bistonines give unmistakeable indications 

 of their Boarmiine trend — as I have emphasised by terming 

 them the Boarmioid Bistonines— none ever carried their 

 tendencies further than certain genital structures, exhibited 

 particularly in the valves. 



Nacophora, however, combines the two features of the 

 Boarmioid genitalia and a veritable Boarmiine foveal depression 

 and, by so doing, puts us in possession of the necessary tran- 

 sition between the two subfamilies. 



But the range of these equivocal genera is purely American 

 and so, therefore, is inevitably its origin, and consequently 

 the centre of the whole of the wide-spread Boarmiince must 

 be localised in the New World. Still we must not bind ourselves 

 to the idea that this Nacophora group is without its allies 

 elsewhere, even if not very near ones, for in its lack of the 

 second pair of posterior tibial spurs and its superficial — nay 

 its more delicate characters— it approaches Biston as typified 

 by the primitive B. straiaria. Likewise, this approach is 

 much more than coincidence, it is genetic. In spite of this, 

 the remarkable fact emerges that, whilst Biston is confined to 

 the Palaearctic and Indian regions, the Nacophora trio is a 

 development of the Nearctic and Neotropical Zoogeographical 



1918 May 1. 



