488 WHEELER. 



From the Scilian amber, which is of later, Miocene age, Emery (1891) 

 has described 14 ants representing 13 genera, 11 of which are still 

 extant, viz: Ectatomma, Ponera, Cataulacus, Podomyrma (subgen. 

 Acrostigma) , Aeromyrma, Creinatogaster , Tajnnorna, Techno my rmex, 

 Plagiolepis, Gesomyrmex and Oecophylla. Heer (1848, 1849) had 

 previously described a number of ants from the Miocene shales of 

 Oeningen and Radoboj, but owing to the imperfectly developed 

 taxonoraic categories of his day, referred them to such generalized 

 genera as Formica, Ponera and Myrmica. Mayr (1867), however, 

 examined many of Heer's types from Radoboj and was able to recog- 

 nize among them representatives of the following modern or extant 

 genera: Aphaenogaster, Leptothorax, Liometopum, DoJichoderus (sub- 

 gen. Hypodinea), Lasius, Formica, Oecophylla and Camponotus. 

 Among several thousand ants from Florissant, Colorado, also of 

 Miocene age, I am now able to recognize specimens belonging to the 

 recent genera Pheidole, Crematogaster, Aphaenogaster, Liometopum, 

 Dolichoderus (subgen. Hypodinea), Lasius, Formica and Camponotus, 

 in addition to a few extinct genera (e. g. Agroecomyrmex) . It is evi- 

 dent, therefore, that a large number of important ant genera of the 

 present had been developed by early Tertiary times, and as the species 

 representing these genera are quite as highly specialized as their 

 existing congeners, I believe that we must assume that their genera 

 go back at least to the Basic Eocene or even to the Upper Cretaceous. 

 And since these genera clearly represent four of the five subfamilies 

 of living ants, and among them the most highly specialized subfamily, 

 the Camponotinae, we are justified in assuming that the subfamilies 

 of the Formicidae were differentiated during the Mesozoic, probably 

 as early as the Jurassic or Triassic. This assumption is in general 

 accord with the opinions of Emery (1893) and Handlirsch (1913). 

 According to the latter " we know today that by the end of the Cre- 

 taceous all the main groups of insects had been completed, that the 

 species living today arose not later than the Pleistocene and the 

 majority of them in the Pleiocene and in certain cases go back even to 

 the Oligocene. The present genera were certainly nearly all completed 

 in the late Tertiary, many of them already in the Oligocene and per- 

 haps some of them in the Upper Cretaceous." He believes (1909) 

 that the Formicidae as a family could scarcely have originated before 

 the Upper Cretaceous. I am inclined to believe that these estimates, 

 at least as far as the ants are concerned, are too conservative. If I 

 understand Emery correctly, his estimates are somewhat closer to 

 my own, for he is inclined to assign the genera of the oldest subfamily. 



