While search for fossils at Conger Springs, Utah I found lots of examples of these little brachiopods called Eumetria costata. They are small shells that are longer than wide with the widest point about midway between the umbo and the anterior margins. Each valve is roughly equally convex and has around 20 radiating costae on the surface. The umbo extends beyond the brachial valve and curves slightly to the point where the circular formen opening is located.
Specimen #1 - Brachial valve
Specimen #2 -Brachial valve
I used the reference "Geology of Millard County, Utah", Lehi F. Hintze & Fitzhugh D. Davis, 2003 pg. 106, fig.142 to identify these brachiopods. These
specimens came from the Chainman formation at Conger Springs (west of Delta), Utah and are
Carboniferous (Mississippian epoch, Visean stage of the ICS or
Mississippian period, Chesterian stage in the US) in age.