Land snails are among the most abundant terrestrial invertebrates preserved in the Quaternary continental sedimentary record, ranging geographically from the Tropics to the high Arctic tundra. The oxygen (d18O) isotopic composition of these shells have the potential to provide invaluable paleoenvironmental information across space and time. However, reliable paleoenvironmental inferences from fossil and sub-fossil shells require a detailed modern calibration and validation assessment if the taxa and locality have not been investigated for this purpose before. The bulk of published calibration studies has focused on the middle latitudes of the northern hemisphere whereas tropical latitudes have received minimal attention. This thesis investigates the lowest latitude record of modern land snails from the northern hemisphere and sets the foundation for future paleoenvironmental research in the Tropics using land snails. Four small (<10 mm) species of modern land snails from Trinidad Island (latitude: 10.6918° N, longitude: 61.2225° W) were collected along an east-to-west environmental gradient, isotopically analyzed, and compared to instrument and modeled climate data. Results indicate that while three species overlapped in d18O values, Succinea specimens were consistently higher in d18O. Thus, mixing of snail species in Trinidad may complicate paleoenvironmental inferences. No significant isotopic variations were documented between coastal and inland sites, suggesting similar precipitation d18O values along the transect. The d18O values of snails from Trinidad primarily track the local rain d18O values with a high degree of accuracy, and therefore, ancient shells of these species may be used as proxies for rain d18O throughout the Quaternary in Trinidad and other nearby Caribbean islands. The integration of new d18O values from Trinidad shells presented here with published data of snails across North America reinforces previous observations that land snails mimic variations of precipitation d18O values at local and global spatial scales. Advisors/Committee Members: Yanes, Yurena (Committee Chair).