Some inarticulate brachiopod fossils are uncommon because the shell was made of phosphate instead of Calcite and thus they break apart more quickly. When you do find them they are obvious for the black color of the shell. Here are some Orbiculoidea media specimens that I found at the Penn Dixie site near Blasdell, NY.
Specimen #2, wet to show detail a little better.
Both specimens came from the Windom shale mbr. of the Moscow Formation (Devonian, Givetian stage).