Peabody Academy ov Science, 



Salem, Mass., August 10, 1875. 



Dear Sik : I beg leave to transmit to you a monographical account of 

 the North American species of Geometrid moths. The material which was 

 collected by Lieut. W. L. Carpenter, in Colorado, in 1873, while attached to 

 your party, and by others in the same Territory, added to extensive collec- 

 tions received from the Pacific Slates, as well as the Atlantic States, have 

 made me anxious to treat the subject more thoroughly, and enlarge upon the 

 slight sketch published in your Annual Report for 1874. 



That I can do this in the present fonn is due to your enlightened inter- 

 est in the connection of biological with geological and geographical science. 

 By an attentive study of the insect fauna of the plateaus and mountains of 

 Colorado and adjoining Territories, we are led to comparative studies of the 

 physical features of those regions with the elevated plate; us of Asia. The 

 comparatively few specimens previously received from Colorado indicate # a 

 similarity in its fauna to the Ural and Altai Mountains, most striking and 

 unexpected to myself, and perhaps to most persons. 



Besides the relations to comparative physical geography and the geo- 

 graphical distribution of animals, it is believed that an extended examination 

 of the existing insects of the Western States and Territories will throw light 

 on the extinct forms which abound in the Tertiary formation in those regions, 

 and which have been partially worked up by Mr. S. H. Scudder, the eminent 

 palentomologist, on materials discovered within the limits of Colorado and 

 Utah. For this purpose in part, at least, -much attention has been devoted 

 in the illustrations accompanying this report to the venation of the wings of 

 each genus of the family, as well as to the anatomy of the hard [tarts of these 

 insects which are more likely to be preserved fossil. 



From an economical point of view, a systematic account of the species 



of this family, comprising the measuring or span worms, so many of which 



are injurious to vegetation, will, it is hoped, prove useful to agriculturists; 



and it is believed that a volume on these injurious insects, largely represented 



Iph 



