A survey of the landsnails inhabiting the 20.5-hectare portion of Chesapeake and Ohio Canal National Historic Park formerly owned by the Washington Biologists' Field Club was conducted. Twelve stations, representing all major habitat types present, were intensively studied, and general collecting was done throughout the area. Twenty-five species of snails and slugs representing 12 families were documented. Survey of the literature and pertinent museum collections documented very little change in the composition of the gastropod community over the past 100 years, despite vegetation community succession of the property from largely open field to mature forest. Of nine species known historically from the study area, only one was not found during this survey. Although the mollusk community was diverse, the number of small species was less than expected. This may be the result of the near absence of a leaf litter/humus layer. The absence of those forest floor layers from the study area may be due to the presence of a large population of the introduced Asiatic earthworm, Amynthras agrestis. Regular inundation of flood plain areas along the Potomac River appears to depress or eliminate discrete colonies of land snails.