IQ William Morton Wheeler. 



should expect, if the tropical preceded the boreal forms as the vanish- 

 ing survivors of an ancient and once dominant fauna, but if the boreal 

 forms had been brought down by rivers or torrents from higher alti- 

 tudes or latitudes, one could hardly expect them to outnumber the 

 specimens from the lowlands. 



The foregoing cases of simultaneous inclusion of different spe- 

 cies are, of course, too meager to give us any adequate solution of 

 the questions I have been considering, but they show that such a 

 solution may be possible sometime in the future. At any rate they 

 suffice to prove the desirability of recording all cases of simultaneous 

 inclusion as the amber material accumulates in collections and of not 

 isolating specimens in separate pieces of amber till the associated 

 species have been recorded. 



That the mixed tropical and boreal character of the European 

 ant fauna lingered on through the Miocene in Central and Southern 

 Europe is demonstrated by the species in the formations of Oeningen 

 and Radoboj and the inclusions in the Sicilian amber. This last 

 formation, indeed, is almost purely tropical, with such genera as 

 Cataiilacus, Meranoplus^), Hypoyomyrmex, Podomyrma, Leptomyrmula^ 

 Gesomyrmex, (Ecophylla, Ectatomma, Technomyrmex and Aeromyrma. 

 In the Pleistocene the tropical components disappeared, at least from 

 the fauna of Northern and Central Europe, leaving only the palearctic 

 forms mostly congeneric or even cospecific with nearctic forms, and 

 of these only a few have survived the Glacial Epoch. During this 

 period the region in which the luxuriant ant-fauna of the Baltic amber 

 flourished must have been completely sterilized and has only since 

 been repeopled with a scant fauna from southern Europe. The mea- 

 gerness of the surviving fauna in the region formerly covered by the 

 amber forests may be estimated from the work of Adlerz on the ants 

 of Sweden^). This author cites only 12 genera with 35 species, as 

 follows: 



Myrmica (6) Anergates (1) 



Solenopsis (1) Tapinoma (1) 



Formicoxenus (1) Lasius (6) 



Harpagoxenus (1) Formica (11) 



^) In a recent paper Emery (Le origin! e le migrazioni della fauna mirmecologica 

 di Europa. Rendic. Ses. R. Accad. Sci. 1st. Bologna 1913 pp. 29 — 46) refers to this 

 genus a male specimen which he described as a Crematogaster. 



1) Myrmecologiska Studier. II Svenska Myror och deras Lefnadforhallanden. 

 Bih. till K. Svenska Vet.-Akad. Handl. 11, 18, 1886, pp. 1—329 7 plates. 



