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
Karl Shell the overlapping generations literature (and was perhaps the first to refer to the overlapping generations model by its modern name). The overlapping generations model is now a workhorse in modern macroeconomics and monetary economics. Karl Shell is also co-inventor (with David Cass) of the concept of sunspot equilibrium (and sunspots). Karl Shell Karl Shell (born May 10, 1938) is an American theoretical economist, specializing in macroeconomics and monetary economics. Shell received an A.B. in mathematics from Princeton University in 1960. He earned his Ph.D. in economics in 1965 at Stanford University, where he studied under Nobel Prize in Economics winner