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The gastropod shell is a composite composed of minerals and shell matrix proteins (SMPs). SMPs have been identified by proteomics in many molluscs, but few have been studied in detail. Open questions include (1) what gene regulatory networks regulate SMP expression, (2) what roles individual SMPs play in biomineralization, and (3) how the complement of SMPs changes over development. These questions are best addressed in a species in which gene perturbation studies are available; one such species is the slipper snail, Crepidula fornicata. Here, SEM and pXRD analysis demonstrated that the adult shell of C. fornicata exhibits crossed lamellar microstructure and is composed of aragonite. Using high-throughput proteomics we identified 185 SMPs occluded within the adult shell. Over half of the proteins in the shell proteome have known biomineralization domains, while at least 10% have no homologs in public databases. Differential gene expression analysis identified 20 SMP genes that are up-regulated in the shell-producing mantle tissue. Over half of these 20 SMPs are expressed during development with two, CfSMP1 and CfSMP2, expressed exclusively in the shell gland. Together, the description of the shell microstructure and a list of SMPs now sets the stage for studying the consequences of SMP gene knockdowns in molluscs.