One of the most ubiquitous fossils associated with the Devonian period is the brachiopod Mucrospirifer. This is a very prolific genus and also very variable in it's appearance. Generally it has a half moon shape with the hinge line extending long past the main body of the shell creating a look like a wing. Like many other genus from the order Spiriferida, the body of the shell has a wrinkled appearance with folds extending from the hinge line out to the edge of the shell like rays of sunlight and a prominent central sulcus (fold or depression). Some specimens have a short, fat body and others a much more elongate look. The Genus first appears early within the Devonian and dies out by the end during the Famennian stage. It was first named by the eminent naturalist from New York State, Amadeus William Grabeau (1870-1946) in 1931.
Here is a specimen from the Widder formation at Arkona with lots of Spirorbis attached to the shell:
Another that shows damage and healing to one side of the shell:
An internal mold of one valve from the Mahantango formation:
A plate from the Stony Creek member of the Trimmers Rock Formation with a good specimen that shows how long the "wings" could get:
Another Mahantango piece with a large specimen that is 3" wide at the tips:
These are some very delicate shells on a limestone matrix from the Hungry Hollow member of the Widder Formation at Arkona. Note how elongated the body gets: