Dicoelosia (King 1850) is truly a unique looking brachiopod. The shell has grown into two "lobes" rather than a single rounded shell. I never saw anything like this growth pattern until I saw specimens of the genera Pygope from the Jurassic and Cretaceous of Europe. The specimen shown below is possibly D. varica based on the book "Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region" 1958 Thomas Amsden and Arthur Boucot, Oklahoma Geological Survey, Bulletin 78 pgs:51-54.
I have two specimens of this species and they are really small (4-5mm). The above pictures were taken with my Carson Zorb digital "microscope" as I would not be able to get any detail with my regular Canon SX110IS. This specimen came from an old estate collection of fossils that were collected in the 1960's to 1970's from the Haragan Formation at White Mound, OK. The Haragan formation is thought to range from the upper Silurain, 418mya, to the lower Devonian, 411mya ( Pridoli to Lochkovian). This would correspond to the Birdsong shale of Tennessee and the Helderberg Fauna of New York, Pennsylvania and Maryland.