1978] Burnham — Social Insects in Fossil Record 105 
same position on each. This demonstrates almost certainly that by 
the Lower Oligocene mites had acquired distinct preferences for 
attachment on specific regions of their host’s integument. 
Almost as valuable as the Baltic Amber in providing a large and 
diverse assemblage of fossil ants is the Upper Oligocene deposit in 
Florissant, Colorado, studied by Carpenter (1930). The ant fauna of 
this deposit is strikingly similar to that of the Baltic Amber in many 
respects. It is interesting to note that roughly the same percentage of 
extant genera is found in both places; in the Florissant Shales this 
figure is given as 60 percent (Carpenter, 1930), in the Baltic Amber 
56 percent (Wheeler, 1914). Iridomyrmex is clearly a dominant 
genus in the Baltic Amber, and although not so common in the 
Florissant Shales, a closely allied genus, Protazteca, comprises more 
than 25 percent of all specimens (Brown, 1973). 
Another similarity between the two deposits is the relative 
percentages of the various subfamilies. As in the amber, the 
Dolichoderinae are predominant, comprising 60 percent of the total 
number of ants. The Formicinae comprise another 25 to 30 percent, 
and the Myrmicinae in each deposit are represented by five percent 
or less of the total specimens. This suggests that the ant fauna in the 
northern hemisphere was essentially homogenous during the Oli- 
gocene. 
The remaining deposits of Oligocene age from which ants have 
been described are of relatively minor importance. Most of the 
specimens are fragmentary and the determinations dubious; never- 
theless, a mention of them is certainly necessary. Specimens from 
Gurnet Bay, Isle of Wight, England, have been studied by Cockerell 
(1915) and Donisthorpe (1920). Cockerell described eight species of 
ants from this deposit but, because his generic determinations are 
based chiefly on highly variable measurements of wing fragments, 
they are of dubious significance. Donisthorpe examined a total of 
eight genera and fourteen species belonging to the subfamilies 
Ponerinae, Dolichoderinae, and Formicinae. Surprising is the large 
number of Oecophylla workers recovered (245); this genus is now 
restricted to Africa, India, and Australia, and is much more 
numerous in the Gurnet Bay deposit than in the Baltic Amber or 
Florissant Shales. This might be due to the difference in latitude 
between the deposits which would account for a warmer climate at 
Gurnet Bay later into the Tertiary than at the more northern 
deposits. 
