The SEM observation on a conch’s shell shows that the shell is a kind of laminated bioceramic composite composed of aragonite layers and organic matrix. Each aragonite layer is parallel with 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 orientations of the sheets in different layers are different and these aragonite sheets compose various layups. A kind of lambdoidal layup is found. The maximum pullout force of the lambdoidal layup is analyzed based on its representative model. The result shows that the lambdoidal layup can markedly increase the pullout force of the layup and improve the fracture toughness of the shell.