Shell money most valued by the Native American tribes of the Pacific Coast from Alaska to northwest California was "Dentalium shell", a species of long narrow marine shelled mollusk, a tusk shell or scaphopod. The tusk shell is naturally open at both ends, and can easily be strung on a thread. This shell money was valued by its length rather than the exact number of shells; the "ligua", the highest denomination in their currency, was a length of about 6 inches. Farther south, in central California and southern California, the shell of the olive snail "Olivella biplicata" was used to make beads
Wampum valued at 9 pence a yard, and "wampom peak" as denoting specifically the more expensive dark purple shell bead, at the rate of 1 shilling and 6 pence (18 pence) per yard. He says that these polished shells with drilled holes are made from the "cunk" (conch), while another currency of lesser value called "roenoke" was fashioned from the cockleshell. The process to make wampum was labor-intensive with stone tools. Only the coastal tribes had sufficient access to the basic shells to make wampum. These factors increased its scarcity and consequent value among the European traders. Dutch colonists began to