8 Zoology of Colorado 



amber. Then we obtained Archimyrmex from the Colorado shales, 

 still more ancient, but clearly of the same alliance. Thus it seems 

 that there existed a race of ants widely spread over the world, 

 which eventually failed except in Australia, where it still prospers. 

 The case may be compared with that of the marsupial mammals, 

 which were formerly world-wide, and now abound in Australia. 

 There are however living marsupials in America, and it may be 

 that some one will discover in the Andes or elsewhere a living 

 member of the bull-dog ant group. Had we been living at the 

 time represented by the shales, we should have noticed especially 

 some very prettily marked and varied insects with broad wings, 

 which might be taken for moths. As a matter of fact they are 

 Fulgoroids, members of the Homoptera, more nearly related to 

 the cicada. Such insects are common in the tropics today, par- 

 ticularly in India, but they have disappeared from Colorado, 

 leaving only some dull and insignificant looking relatives. The 

 preservation of the Fulgoroids is so good, that the patterns of the 

 wings are as distinct as in life, though the bright colors are gone. 

 It is curious that so far we have found no butterflies or moths in 

 these deposits. What at first seemed to be a small moth was seen 

 on closer inspection to be a caddis-fly. The old motto, Naiura 

 maxime miranda est in minimis, is exemplified by a minute fossil 

 fly of the Roan Mountains, only 3.2 millimeters (about an eighth 

 of an inch) long. It is so well preserved that many small details 

 can be seen, indicating that it may well be an ancestor of the 

 modern Agromyzidae. It has been called Eomyza holoptera, and 

 while it is unlike any living fly, its characters are similar to those 

 existing in various related species. Its scientific interest is mainly 

 due to the following facts. Professor T. H. Morgan and his 

 associates in Columbia University have for many years made an 

 intensive study of the genetics of the fruit-fly, Drosophila. They 

 have found very many mutations, and have been able to throw 

 more light on the process of heredity than any previous workers. 

 These classical researches have suggested that new species may arise 

 rather rapidly through mutation, and in general that their evolution 

 may proceed at a rate comparable to that of the mammals. Now 

 the discovery of Eocene Acalyptrate Muscoids brings out the fact 

 that, after all, the essential characters of these flies are extremely 

 ancient, and have not been progressively changing throughout 



