8 INTRODUCTION. By Dr. A. Seitz. 



their resting posture, but have preserved their Jjright colour on the underside as well as on the hindwing, 

 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 Htjblaea., Laphygma, Prodenia, etc., appear in large number at 

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

 all Thysania agrippina, which has the largest expanse of wings of all the known Lepidoptera. 



The Geometrids show a very uniform distribution throughout the world. Their relatively 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 generally 

 duller and darker colours of the temperate climate give place to brighter and often beautifull}^ 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, j^et several species, such as Eugoiiia magnaria (aliiiaria), 

 Hydria midulata, Anagoga puheraria, etc., occur in both without anj' essential differences. 



Among the larger Geometrids, the genera Azelina, Clysia, Oxydia, Prochoerodes and Sahulodes are 

 pariicularh' 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 onljf developed exceptionallj' in the American Geometrids {Opjhtludnwphora); 

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

 coloured bands on a black ground wliich occur in Scordylia, Nelo, Sangala, 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 Cymhidae, are not represented at all in 

 America; others, such as the Nyctemerids, ovAy by a few forms, which might probablj^ be better refeiTed 

 to some other group. It is verj' 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 very numerous geo- 

 graphical puzzles. 



