The W. J. Zinsmeister Collection contains approximately 5510 lots (ca 22,000 specimens) of Cretaceous-Eocene fossil mollusks from Seymour Island, Antarctica and vicinity, including bulk samples from measured Cretaceous-Tertiary (K-T) boundary sections. The collection was assembled over more than three decades by William J. Zinsmeister, professor of geology at Purdue University, and is widely recognized as among the largest and finest in the world from this region. The Zinsmeister Collection is an immense scientific treasure and important resource for research. It is probably the world’s largest fossil collection from Seymour Island, Antarctica, which is one of the world’s most important localities for studying the period of Earth history between the Late Cretaceous and Late Eocene (ca. 80-35 million years ago). The curation and digitization of this collection has been made possible by the support of the National Science Foundation through the Office of Polar Programs (OPP 0944684).