This dataset was used to evaluate isotopic shifts associated with 1) coating shells in paraffin wax using a paraffin-xylene solution, 2) exposure to a xylene-only solution, and 3) exposure to xylene rinses to remove previously applied paraffin from periostracum. For each of the three experiments, we used five specimens of each of two target species (L. siliquoidea and O. reflexa). We collected three replicate samples under both untreated (control) and treated conditions from each specimen. We analyzed all samples using a continuous flow Costech Elemental Analyzer coupled to a Thermo Scientific Delta V IRMS via a Thermo Scientific ConFlo IV interface. For each replicate, we report δ13C, δ15N, %C, and %N values. For each individual shell, we also report the mean, median, minimum, maximum, and range of δ13C, %C, δ15N, and %N values.