8 
Psyche 
[March 
theryi ” side by side and designated as K. 6397, in my paper 
on the “Ants of the Baltic Amber” (1914). The large 
worker, which measures fully 7.5 mm., is very clear, but the 
head of the small worker, which measures only 4 mm., is 
obscured by a film and some bubbles of air. I have now had the 
block cut down and repolished, so that the head of the small 
individual is more clearly visible. It proves to belong to the 
form which I called D. mayri, and is really a media of the 
same species as the large (maxima) worker. The latter has 
small but very distinct ocelli, but none can be detected in 
the companion specimen. Since G. annectens is clearly inter- 
mediate between D. mayri and G. hoernesi, the former is, in all 
probability the large minima, whereas the latter represents 
the small minima of Mayr’s species. I am, therefore, of the 
opinion that all the specimens of Dimorphomyrmex and 
Gesomyrmex in the Baltic amber belong to a single poly- 
morphic species, which should be known as G. hoernesi Mayr. 1 
This is of considerable interest, because it shows that as far 
back as the Lower Oligocene one Formicine ant had not 
only reached a high degree of specialization in the reduction 
of the number of antennal joints of the worker from 12 to 8, 
but that this caste had become as polymorphic as it is in the 
living species of the genus now confined to Indonesia and 
Southern China. And conversely, the very rare and sporadic 
occurrence of these forms shows that they are really living 
fossils which have undergone no significant modification 
since the Early Tertiary. 
The workers collected by Dr. Kalshoven were accom- 
panied by several milk-white larvae of different sizes and a 
single semipupa. The larvae resemble those of other Formi- 
cinae in shape, but are almost hairless. The head is very small 
and subglobular, the mandibles minute, with only an apical 
tooth, which is drawn out into a slender, acute point. The 
semipupa measures a little over 7 mm. and is not enclosed in 
a cocoon. We must infer, therefore, that the pupae of Geso- 
myrmex are naked as in a few other genera of Formicinae. 
((Ecophylla, Prenolepis, Paratrechina) . The semipupa is 
clearly a male. It has well-developed wing-pads and rudi- 
ments of the genital valves, and the imaginal head (Fig. 1, k) 
iCompare my figures 50-53 in “The Ants of the Baltic Amber.” 
