1985] 
Wilson — Cretaceous and Eocene amber ants 
209 
contributes new evidence that the most primitive known ant sub- 
family, the Sphecomyrminae, was widespread through the northern 
half of the world during the latter half of the Cretaceous Period. 
Eocenidris, new genus 
Diagnosis (worker). An Eocene myrmicine genus distinguished 
from all other known genera by the following combination of 
worker traits: very small size; relatively narrow mandibles with 
oblique masticatory border bearing 6 irregularly shaped teeth; 
smoothly and strongly convex promesonotum apparently undivided 
by transverse sutures; propodeum armed with short, stout spines; 
and incrassate femora and tibiae. 
Type species: Eocenidris crassa. 
Eocenidris crassa, new species 
(Fig. 3) 
Diagnosis (worker). Distinguished from other known ants by 
the combined traits just cited in the generic diagnosis. 
Holotype worker. Head Width 0.40 mm; length of alitrunk 
from the anterior edge of pronotal collar to posterior edge of pro- 
podeal flange, 0.50 mm. Other visible features as shown in Fig. 3. 
The antennae and eyes are either missing or positioned in a way so 
as not to be made visible without endangering the specimen through 
fragmentation. Similarly, the posterior part of the abdomen could 
not be studied. In amber of the Middle Eocene (Claiborne) of Mal- 
vern, Arkansas. Collected by R. H. Mapes (see Saunders et al., 1974). 
Deposited in the Museum of Comparative Zoology, Harvard 
University. 
Eocenidris crassa is a typical myrmicine, possessing a set of traits 
that are advanced relative to those of Agraecomyrmex of the Baltic 
amber, the modern genera Hylomyrma and Myrmica, and other 
Myrmicinae considered primitive. Its existence demonstrates con- 
clusively that a substantial amount of evolution had occurred within 
the subfamily, hence within the ants as a whole, by the middle of the 
Eocene. 
E. crassa superficially resembles the species of the modern Neo- 
tropical genus Oxyepoecus, which are in some cases inquilines of 
Pheidole and Solenopsis, but it lacks ventral processes on either the 
