An accumulation of molluscan shells. This collection can vary from a basket of shells to a massive amount of shells, all of which are (typically) cataloged with a taxonomic name and (more importantly) collection data. Professional collections are maintained at a variety of museums, for example the United States National Museum (USNM), Philadelphia Academy of Natural Sciences (ANS), etc. Many "shell collections" are better classified as mollusc collections because they contain the preserved shelless molluscs as well. Often the professional collections are repository sites for TYPE SPECIMENS. Some "shell" collections (or sub-collections) may be entirely of a variety of OPERCULA.