This image is of a partial fossil of a spiny Platyceras dumosum gastropod fossil. Found in Louisville, Kentucky in the Devonian Period Jeffersonville Limestone. My cousin found this to add to maybe the 2-3 others he has found in the last year or so. He has prepped this one a little bit since finding it but the spines on it are impressive. Quite the little porcupine of the sea.
Another picture of the specimen shown earlier but more on the intact spine side.
This image is from the book Kentucky Fossil Shells - A Monograph of the Fossil Shells of the Silurian and Devonian Rocks of Kentucky by Henry Nettelroth, 1889, Frankfort, Kentucky, Kentucky Geological Survey, Plate XXIII, Figure 2 of the Platyceras dumosum.
He also found a negative image at a different time of another Platyceras again from the Jeffersonville Limestone.