1917] Fossil Insects 15 



where it carries parasites which cause fatal diseases to man and 

 animals. No less than four species of tsetse flies have been 

 found fossil at Florissant; and the extraordinary thing is, that 

 these alone represent the higher Muscoids in the fauna, there 

 being no true Muscidas, no Tachinidae, Dexiidas or Sarcophagidse. 

 Anthomyiidae and various acalyptrate families appear to be 

 rather common. Bombyliidas are abundant and very varied, 

 consisting of twelve genera now extinct, a doubtful Geron, and 

 a species of the living but rare and widely scattered genus 

 Dolichomyia. It is possible that the Bombyliidas then occupied, 

 as parasites, the position now chiefly taken by the Tachinidae. 

 The Anthracine Bombyliids, now so prominent in the Rocky 

 Mountain fauna, appear to have been entirely absent; their 

 advent during the later part of the Miocene may have been 

 one of the main causes of the disappearance of so many of the 

 Florissant genera, though the competition of the Tachinids 

 must also have been important. We get here a glimpse of the 

 drama of insect life; the development of a series of types 

 occupying a definite place in the scheme of nature, and their 

 replacement by other more vigorous or aggressive forms, com- 

 ing from some remote region of the world. Another astonishing 

 Florissant fossil, discovered by Mr. S. A. Rohwer, is a species of 

 Nemopteridae, those remarkable insects with long narrow hind 

 wings, expanded at the end. I could not separate the species 

 from the Old World genus Halter; but Navas, after examining 

 my type, concluded that a distinct genus was indicated. He 

 accordingly named it after Pere Marquette, and the insect 

 becomes Marquettia americana (Ckll.) 



Professor Wickham, who has occupied himself with the 

 Florissant Coleoptera for several years, is now able to enumerate 

 nearly 570 species; his latest paper, on the Elateridse, records 

 43 members of that family, as against 23 species described from 

 all other deposits of the world combined. The beetle fauna 

 has an entirely Holarctic facies, though extinct genera are 

 fairly numerous. The Rhynchophora are extraordinarily numer- 

 ous; very much more so than in the Miocene of Europe. On 

 the other hand, the Chrysomelidse are relatively scarce, and 

 there are no Histeridas or Cicindelidae. Among the causes 

 which have led to the contraction of the Rocky Mountain 

 weevil-fauna since the Miocene, must evidently be the great 

 reduction in the number of genera of woody plants; the total 



