COCKERELL: FOSSIL HYMENOPTERA FROM FLORISSANT. 35 



mouth-parts, etc. Tlie evolution of the bees has gone on principally in 

 the development of the mouth-structures, the venation remaining nearly 

 as in the fossorial wasps, or at any rate not undergoing any radical 

 changes. Hence it may be that if we could see the tongue, palpi, etc., of 

 the Florissant species of Halictus, Andrena, Anthidium, etc., we should be 

 compelled to remove them from those genera; but the agreement of the 

 wings and general appearance is such that I feel as confident of the gen- 

 eric determinations as is possible under the circumstances. 



The families represented are exactly those dominant to-day in North 

 America, and the absence of certain groups must no doubt be regarded 

 as accidental. 



One would infer from the evidence afforded by the Florissant Hymen- 

 optera, that the genera of this group are more persistent in time than the 

 genera of Mammalia, but less so than those of flowering plants, espe- 

 cially trees. The same conclusions might be reached independently by 

 a study of geographical distribution, at least so far as they relate to mam- 

 mals and Hymenoptera. No doubt the genera of Hymenoptera are 

 more widespread than some other groups of organisms which may 

 possess greater antiquity, owing to the ready locomotion of the 

 former. 



Unfortunately, we have no series of mammals known to be of the same 

 age as the Florissant shales. The White Eiver beds, which Matthew 

 (1899) calls Oligocene, have produced in Colorado some 63 species of 

 mammals, all referred to extinct genera except a few pertaining to Didel- 

 phys and Sciurus. These animals, very differently from the Florissant 

 Hymenoptera, if produced alive would excite the greatest amazement. 

 Species of Titanotheriidae, Elotheriidae, Hyaenodontidae, Rhinocerotidae, 

 Camelidae, Oreodontidae, etc., would cause bewilderment to a zoologist to- 

 day. Even those pertaining to families still inhabiting the earth would 

 for the most part look quite strange to us, being of extinct genera. 



The Loup Fork beds, referred to the Upper Miocene, have produced 

 in Colorado about 28 species of mammals, but even these are nearly 

 all of extinct genera, though only two, possibly three, of the families are 

 extinct. We note the arrival of the Elephantidae, and the great abun- 

 dance and variety of Equidae. As the Florissant shales are certainly not 

 later than the Loup Fork, but doubtless earlier, the opinion that the 

 families and genera of aculeate Hymenoptera are much more conservative 

 than those of Mammalia seems justified. The same facts lead us to 

 believe that the differences noted by Scudder between the insects of the 

 Green River series and Florissant surely indicate a considerable difference 



