CENOZOIC ERA: AGE OF MAMMALS 



629 



mud. The finely laminated shales of Oeningen, on the Lake of Con- 

 stance, Florissant, in Colorado, and elsewhere have yielded hundreds 

 of specimens. 



Horseflies, Tsetse Flies, and Ants. — The presence of horseflies 

 very similar to living forms in the Miocene deposits (Florissant, 

 Colorado) is interesting, as it shows that, even at that early date, 



Fig. 559. — Tertiary pelecypods : A, Melina (Perna) maxillata (Miocene) ; 

 B, Arcoptera aviculceformis (Pliocene). (Maryland Geol. Surv.) 



the horse was probably tormented by this insect. Although the 

 horse has changed radically, the flies have remained practically the 

 same. In the same deposits (Florissant, Colorado) the tsetse flies 

 occur. '' The exquisitely preserved ants of the Baltic amber, be- 

 longing to the Lower Oligocene formation, are in all respects like 

 existing ants. All of them belong to existing subfamilies, most of 

 them even to existing genera, and a few of them are practically indis- 



