46 
Psyche 
[Vol. 90 
tunately, the poor preservation of the one specimen known 
pjecludes a more detailed species description. 
Geological range: Westphalian D. Occurrence: Mazon Creek, 
Illinois, U.S.A. 
Holotype: YPM 38. Specimen examined. Obverse and reverse 
halves. 
Depositional Environment 
For most of this century, Mazon Creek and Commentry have 
reigned as the two major localities of Upper Carboniferous insects (a 
third locality has just been added to this list; see Burnham, 1981). 
Both have provided large numbers of superbly preserved specimens 
and have contributed greatly to our understanding of early insect 
evolution. Because the family under consideration is represented at 
both places, a comparison of their geological history is warranted. 
Roughly three hundred million years ago, in the Stephanian 
Stage of the Upper Carboniferous, the Commentry Coal Basin was 
a shallow lake — 9.6 km long, 3.2 km wide, and encircled by moun- 
tains (Fayol, 1887; Stevenson, 1909). Two principal streams de- 
scended from the surrounding mountains into the lake, where deltaic 
swamps formed from the deposition of fine-grained sediments. 
These were, in many respects, typical coal swamps, characterized by 
Cordaites, and, in lesser numbers, other coal swamp flora such as 
Lepidodendron and Stigmaria. Fossilization at the site was almost 
instantaneous, the result of flooding that deposited massive amounts 
of sediment in the lake and bordering swamp. The remarkable pres- 
ervation of the Commentry insects would not have been .possible 
without their immediate burial under these catastrophic conditions, 
and it is assumed that they were buried with minimal post-mortem 
transportation. 
The first fossils at Commentry were discovered in the mid- 
nineteenth century as a result of extensive coal exploration in the 
central region of France, and were made accessible to collectors 
only because of intense mining activity in the area. Once the coal 
supply began to diminish, about 1915, the mines were closed down 
and filled in, and further fossil collecting prohibited. For an histori- 
cal account of the Commentry collections and a review of the litera- 
ture on Commentry insects, see Carpenter (1943). 
