Models of prehistoric seasonal settlement movements along the southeast U. S. coast have been based on ecological and historical documents. Few direct measurements of archaeological data have been applied towards testing these models. A method for the determination of season of oyster collection in archaeological middens has been recently forwarded by a number of authors. An alternative and complementary method of determining season of collection of oysters that employs the measurement of a parasitic gastropod, the impressed odostome (<i>Boonea impressa</i>=<i>Odostomia impressa</i>) is forwarded. The method is applied to two case studies of late prehistoric contexts at Meeting House Field, St. Catherines Island, Georgia and Harrison Homestead, Amelia Island, Florida.