16 Amials Entomological Society of America [Vol. X, 



elimination of the figs, magnolias, chestnuts, elms, Ailanthus, 

 and various other kinds of trees. This change in the vegetation 

 would necessarily affect thousands of plant-feeding insects, 

 while the climatic changes giving rise to it would favor the 

 increase of many genera. Thus, the more we study the Miocene 

 insects of Colorado in comparison with those of today, the 

 more evident it becomes that the differences observed are due, 

 not so much to any definite forward evolution, as to migrations 

 and the extinction of a certain number of genera. It is a very 

 striking fact, however, that in particular groups, such as 

 Aphididae and Bombyliidce, the genera are practically or quite 

 all extinct, while in others they are little different from those 

 now inhabiting North America. The most conspicuous contrast 

 between Florissant and the Baltic amber is seen in the bees. 

 All the amber bees are of extinct genera; but of the 28 species 

 of Florissant bees, only eight belong to extinct genera. Wheeler 

 has recorded evidence that as far back as the Baltic amber, 

 perhaps a couple of million years, the ants had many of the 

 specialized habits they have today. Similarly at Florissant, we 

 find that various kinds of gall-insects made galls as they do now, 

 and leaf -cutting bees cut leaves in exactly the same manner.* 

 Species of Ficus, both leaves and fruit, have been uncovered; 

 and also a genuine fig-insect, which doubtless brought about 

 fertilization as fig-insects do today. 



From Florissant times up to the Pleistocene, we have no 

 knowledge of the character of the North American insect-fauna. 

 From the Pleistocene, however, a fairly large assemblage of 

 beetles is known, and there is every reason to suppose that it 

 will be greatly increased when more systematic search is made. 

 The latest discovery of Post-tertiary beetles has been made in 

 Florida; some specimens which reached me from Dr. E. H. 

 Sellards the other day have been forwarded to Professor Wick- 

 ham, who will report upon them. 



The study of fossil insects adds another dimension, as it 

 were, to the edifice of entomological science, and throws light 

 on the broad problems of evolution. When insect remains in the 



*Berry, in his excellent work on the Lower Eocene Floras of S. E. North 

 America, recently published by the U. S. Geological Survey, figures a leaf of 

 Icacorea showing numerous holes, and remarks that may indicate the work of a 

 species of Megachilidae. The work is, however, entirely different from that of 

 the leaf-cutting bees, and it would be a mechanical impossibility for any one of 

 them to riddle a leaf in the manner shown. 



