Molluscan shell is strong, stiff, tough and shows an erose fracture surface when it is broken. In this research, the SEM observation on a Rufescens’s shell shows that the shell consists of aragonite layers and collagen matrix. Each aragonite layer is parallel to the surface of the shell and consists of many thin aragonite sheets. These aragonite sheets are perpendicular to the layer where they are located. The observation also shows that the direction of the sheets in different layer is various and a kind of herringbone distribution is found. The maximum pullout force of the herringbone distribution is analyzed based on its representative model, and it shows that the herringbone distribution can markedly increase the pullout force of the distribution and improve the fracture toughness of the shell.