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
Two Row Wampum Treaty significant, and it is the two-row wampum that is understood to represent this conception most powerfully, with two rows of purple wampum beads against a background of white beads, each row representing a parallel river, down which the respective vessels of each people travel, independently but in mutual support of each other. The question of what materials — wampum or otherwise — were exchanged at the initial negotiations of the treaty cannot be answered definitively. While it is possible that a two-row wampum belt featured in the initial treaty negotiations, there is no documentary evidence to support this claim. There