This series consists of small reports on research topics that were not expected to be re-examined. They were more inexpensively produced than special reports, owing to the more specialized subject matter. Henry H. Gray initiated this series in 1974, suggesting the benefit of a larger 8 ½” x 11” publication format (usually reserved for guidebooks) to display his research. Although occasional papers were initially produced in black and white using the Docutek process, the most recent versions were distributed digitally as downloadable PDFs. All required a full formal review.