Scaphopods are the smallest of the major mollusc classes, with a tube-shaped shell open at both ends. The animal lives head-down in sediment, extends fine tentacles called captacula to capture foraminiferans, and draws water through the exposed narrow end. They have no eyes, no gills and no distinct heart.
The shells' regular tapering tube made them convenient to string, and along the Pacific coast of North America Dentalium shells became a recognised currency. Value depended on length, with longer shells worth disproportionately more, and strings were measured against standardised units. Harvesting concentrated around Vancouver Island, and the shells travelled far inland through trade networks, reaching the Plains.
A point often blurred is scale. Dentalium was not a token currency imposed by a state; it was valuable because it was hard to obtain, uniform enough to compare, and durable. The Hudson's Bay Company later imported manufactured imitations, which depressed the value of the real thing, a familiar sequence when an existing exchange medium meets industrial supply.