1983] 
Burnham — Geraridae 
13 
simple or with one bifurcation; CUP simple and parallel to CUA; 
anal area slightly expanded, but unusually reduced for the Orthop- 
teroidea. See fig. 17. 
Diagnosis 
Gerarus may be distinguished from the other genera in the 
Gerandae {Nacekomia, Progenenfonium, Genentonmm and Gerarulus) 
by size (members of this genus are large, fore wing is 40 mm to 55 
mm in length); and the nature of the RS and M veins in the fore 
wing. In Gerarus RS branches two or three times; in Progenentonium, 
it branches at least four times. M in Gerarus is four- or five-branched, 
and either coalesces with RS for a short distance or is connected to 
it by a well-developed cross vein. In contrast, M in Naeekomia is 
distinct from RS, and in Genentonium, M is only three-branched 
and these branches are distinctly parallel to one another. Other 
characters such as the shape of the thorax and number of prothoracic 
spines may ultimately prove important in distinguishing these 
genera from one another, but as yet, we lack the well-preserved 
specimens necessary for separating all four genera in the family on 
the basis of such additional characters. 
Remarks 
Handlirsch (1911:313) characterized Gerarus by its prothorax, 
described as “a broad base, either provided with tubercles or 
smooth, but in every case, produced into a long neck-like part bear- 
ing the head.” While he was correct about the nature of the “neck,” 
he was incorrect in his assessment of the “tubercles,” which were 
presumably present in all adult gerarids as fully produced spines, 
not tubercles. He was also slightly inaccurate in describing the pro- 
thorax as “a broad base.” This study has shown the width of the 
prothorax to vary from 5 mm to 13 mm depending on the species. A 
better description for the genus is one based on wing venation. 
Geological range: Upper Carboniferous — Westphalian D to 
Stephanian. Occurrence: Mazon Creek, Illinois, U.S.A.; Com- 
mentry, France. Type species: Gerarus vetus. 
Synonymies 
As indicated in previous pages, clarification of the venation of 
both fore and hind wings has led to several important synonymies. 
A comparison of Sthenaropoda with Gerarus reveals that the vena- 
tional differences lie largely in the number of branches of M and 
