Abstract
The family Syntonopteridae was named by Handlirsch in 1911 for a new genus and species, Syntonoptera schucherti, from the Upper Carboniferous of Mazon Creek, Illinois. Although the unique specimen on which the species was based consisted of only a wing fragment, the presence of several intercalary, triad veins was of unusual interest. During the 75 years that have passed since then, only six additional specimens of the family have been found (Carpenter, 1938, 1944; Richardson, 1956), all of them in the Mazon Creek beds. The latest of these specimens was sent to me for study by Dr. E. S. Richardson, Jr., a few months before his death, and I have only recently had the opportunity to study it and prepare illustrations. While working on this fossil, I decided to reexamine at the same time the other five specimens in the family known to me. A review of these specimens is included here, followed by revised diagnoses of the family and of the two known genera.