This highly decorated shell has a very long name: Kozlowskiellina (Megakozlowskiella) velata. It is related to Kozlowskiellina perlamellosa which is found in the Helderberg fauna of New York. The shell is triangular to half moon shaped with each convex valve featuring coarse plications (generally three on each side of the fold and four on each side of the sulcus). The shell is further decorated with strong concentric growth lamellae. The pedicle valve recurves, extends past the brachial valve and has a wide, triangular interarea and narrow triangular dethyrium.
Compare this specimen to one from the Haragan formation which underlies the Bois d'Arc formation.
I found the specimen shown on this page in the Bois d'Arc formation (Cravatt member) near Clarita, OK which is Devonian in age (Lockhovian stage). The Bois d'Arc and Haragan formations interfinger with each other and are roughly the same age (Devonian, Lockhovian stage). They are both roughly correlative to the Helderberg fauna of New York and thus are contemporaneous with the Coyemans, Kalkberg and New Scotland formations.
"Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region, Part V - Bois d'Arc Articulate Brachiopods " Amsden, 1958, Oklahoma Geological Survey Bulletin 82
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