Representative shell forms of Upper Silurian bivalves from Wenlock and Ludlow formations 插畫檔

This illustration displays three distinct species of ancient marine mollusks, highlighting the diversity of bivalve shell structures during the Upper Silurian period. One specimen features a rounded, globose shape with prominent, intersecting concentric and radiating ridges that create a textured, lattice-like surface. Another variety exhibits an elongated, asymmetrical form with a wing-like projection at the hinge and a surface marked by strong, fanning longitudinal ribs. The third figure shows a more spirally-wound, conical shell with deep, horizontal growth bands, illustrating a morphology that mimics some gastropod forms while retaining its bivalve classification. These specimens, recovered from the Wenlock and Ludlow strata, represent a group of organisms that increasingly diversified in the shallow Paleozoic seas, filling various ecological niches on and within the seafloor sediment.