16 
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 öutnumber the 
specimens from the lowlands. 
The foregoing cases of simultaneous inclnsion of different spe- 
cies are, of course, too meager to give ns 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 accumul ates in collections and of not 
isolating specimens in separate pieces of amber tili 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 
Cataulacus , Meranoylus 1 ), Hyyoyomyrmex, 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. Düring 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 1 ). This author cites only 12 genera with 35 species, as 
follows: 
Myrmica (6) 
Solenopsis (1) 
Formicoxenus (1) 
Harpagoxenus (1) 
Anergates (1) 
Tapinoma (1) 
Lasius (6) 
Formica (11) 
b In a recent paper Emery (Le origini e le migrazioni della fauna mirmecologica 
di Europa. Rendic. Ses. R. Accad. Sei, Ist. Bologna 1913 pp. 29 — 46) refers to this 
genus a male specimen which he described as a Cremcitogaster. 
B Myrmecologiska Studier. II Svenska Myror och deras Lefnadförhallanden. 
Bih. tili K. Svenska Vet.-Akad. Handl. 11, 18, 1886, pp. 1 — 329 7 plates. 
