Planorbiform shell structure and surface ornamentation of Maclurea crenulata from Newfoundland 插畫檔

This scientific illustration presents three views of a fossilized gastropod shell recovered from the Quebec Group in Newfoundland. The specimen exhibits a "planorbiform" or flat-coiled growth habit, characterized by a shell that is nearly flat on one side and deeply concave on the other. The side views show a series of tightly wound whorls decorated with prominent, rhythmic transverse ridges and fine growth lines that follow the curvature of the shell. A cross-sectional or edge-on view highlights the thick, robust nature of the shell wall and the wide, triangular aperture where the living marine snail once emerged. These unique mollusks were specialized inhabitants of the seafloor during the Lower Silurian period and are often used as index fossils to identify specific geological horizons within the North American stratigraphic record.