8 INTKUDUCTIOX. By Dr. A. Smra. 



their resting posture, hut lia\'e preserved tlieir bright colour on the underside as well as on the hindwino' 

 which is concealed beneath the grey forewing. In the tropics of America the Noctuids recede in point of 

 numbers, as only a few groups, such as Hi/blaeu, Luphi/pna, Prodenia, etc., appear in large number at 

 times; however, the western tropical species frequently develop gigantic forms, such as Erebus and before 

 all TInjsania ac/ripjniM, which has the largest ex])anse of wings of all the known Lejiidoptera. 



The Oeometrlds show a very uniform distribution throughout tiie world. Their relativelv weak 

 flight makes them insecure on islands, and is a hindrance and menace to their propagation in the smaller 

 storm-beaten islets. This general rule holds also for America, and so does the other rule, that the generallv 

 duller and darker colours of the temperate climate give place to brighter and often beautifully marked 

 colouring in the warmer regions. As many species extend far northwards, there is a possibility of com- 

 munication between the two hemispheres in respect of their Geometrid fauna; and although there are far 

 fewer Geometrids than Noctuids common to the two, yet several species, such as Eugonia mn^gnaria (ahdarhi), 

 Hydrki imduluta, Anagoga piilneraria, etc., occur in both without any essential differences. 



Among the larger Geometrids, the genera Azelina, Clgsiic, Oxgdia, rrochocrudes and Sabidodes are 

 particularly prominent in America. In their habitus they borrow a good deal from the forms of other 

 groups which inhabit the same region, but without showing any mimetic tendency. As in tlie Eastern 

 Hemisphere, metallic colours are only developed exceptionally in the Amei'ican Geometrids {Ophthcdmophont); 

 on the other hand we are confronted with true American schemes of colour and markings in the brightly 

 coloured bands on a black ground which occur in Snmhjlid, Kr/u, Sanga/x, etc. 



The above is in broad outline a comparative picture of the American fauna and that of the Old 

 World. It ought to be mentioned that some groups, such as the Cgmbidae, are not represented at all in 

 America; others, such as the Nyctemerids, only by a few forms, which might probably be better referred 

 to some other group. It is very strange that the nearest representative of the tropical American genus 

 Urania belongs to South-East Africa; cases like this belong to the at present still ver\' numerous geo- 

 graphical puzzles. 



