Anthracospirifer sp. brachiopod from the Chainman formation of Utah

I believe this next brachiopod fossil is Anthracospirifer sp.. It comes from the Chainman formation at Conger Springs in Utah. The shell is missing part of a "wing" but enough is left to help identify it. The pedicle and brachial valves are equally convex, rectangular shaped and have coarse plications. A sulcus on the pedicle valve corresponds with a single fold on the brachial valve. The pedicle valve has a wide interarea with a recurved beak.

Brachial valve

Anterior

Pedicle valve

Posterior

Profile

There are a number of known species of Anthracospirifer but little literature on what specific forms occur in the Chainman formation. One resource, "Mississippian Stratigraphy of the Diamond Peak Area, Eureka County, Nevada", Brew, David, 1971, Indicates that A. occiduus, A. pellaensis, A. increbescens and A. bifurcatus are found in equivalent strata in Nevada but I can find no clear illustrations of those species or those I find do not match what I have here..

The reference "Brachiopoda of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming.", MacKenzie Gordon, Jr., 1975 lists multiple species of Anthracospirifer, including A. occiduus but none seem to match my specimen.

This specimen came from the Chainman formation at Conger Springs (west of Delta), Utah and is Carboniferous (Mississippian epoch, Visean stage of the ICS or Mississippian period, Chesterian stage in the US) in age.