The lithistid sponge Actinocoelia maeandrina Finks has been found recently in abundance in the Franson member of the Park City formation near Dubois, Wyoming. This new occurrence extends the range of the species from W. Texas, southern New Mexico, northern Arizona, and southern Nevada to western Wyoming. All previous occurrences are from rocks datable as late Leonard or early Guadalupe (Brushy Canyon). The new occurrence suggests that the Franson member in this area is late Leonard or early Guadalupe age. Stratigraphic and paleontologic evidence indicates that the sponge is essentially confined to deposits made in shallow, clear water of normal marine salinity with an abundant shelly fauna. It is likely that this sponge can be used as an index to the upper Leonard to lowermost Guadalupe interval throughout the Cordilleran area, and as an indicator of a shelf or a shell-bank environment.