This image is of a partial fossil of a spiny Platyceras dumosum (Conrad, 1840) gastropod fossil. Found in Louisville, Kentucky USA 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.
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 (1835-1887), 1889, Frankfort, Kentucky, Kentucky Geological Survey, Plate XXIII, Figure 1 of the Platyceras dumosum (Conrad, 1840).
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 (Conrad, 1840).
He also found a negative image at a different time of another Platyceras (Conrad, 1840) again from the Jeffersonville Limestone.