While exploring an outcrop of Silurian aged rock near Mexico, PA I came across some large Ostracod fossils. I was searching for an outcrop of the Keyser formation (Pridoli-Lochkovian) which overlies the Tolonoway formation (Ludfordian-Pridoli). Here is a small plate of limestone with a few of the valves preserved.
The size of the fossils was surprising to me as most species of Ostracod are much smaller, on the order of mm, not cm. The specimen below is about 1.5cm in length.
I was tentative on the ID of the genera as Leperditia as they are known from the Tolonoway formation that I was searching in. I didn't confirm the ID until recently after I received a specimen from a new trading partner in France, Christian. He sent me the below specimen of a Leperditia from the Silurian (Wenlockian) aged rocks of the island of Gotland, Sweden.
The size and shape of the shell are the key indicators you have a Leperditia. Note the straight hingeline along the top edge of the shell also. Ostracods are arthropods from the Crustacea class and thus are related to Crabs, Shrimp and even Barnacles.They live within a bivalved shell swimming freely in the water or crawling along the bottom of the sea.