Some examples of shells' uses in trade are: 

Shell Money: Past and Present: moneyc.html

• Cowrie shells (Cypraea annulus L., and C. moneta L.),
  Collected loose in bags or strung into strands, were the earliest forms of currency used in many countries. The Chinese, so far as we know, were the first people to use cowries as currency. Here, cowries have been found in prehistoric Stone Age sites. Examples of other country's native money-strands are the diwara in New Guinea, rongo in the Melanesian islands and sapisapi in Africa. The image of the cowrie as a type of currency was so strong that the first oval metal coin minted in the Greek colony of Lydia around 670 B.C. was modeled after that shell. By the eighteenth century, approximately 400 million cowries were being traded per year mostly for the purchase of black slaves. By the middle of the nineteenth century, it could take up to 100,000 cowries just to buy a young wife. Inflation, it seems, was the main demise of the cowrie currency.

Hard clamshells and whelks were the shells used to make the North American Indian wampum. Eastern Indians also used the tusk shell Dentalium pretiosum Sowerby (collected on Vancouver Is.! (Canada)) Sowerby, as a trade shell. Wampum continued to be used as money through the first half of the eighteenth century when it finally died out due to counterfeiting and mass production.
Mercenaria mercenaria (Linnaeus, 1758) Hard clamshells, Northern Quahog	Dentalium (Antalis) pretiosum  Indian-money Tusk, I"o*qua shell
See a Hoopa Indian Dentalium Purse

Beads and other ornaments made of  "Spiny Oyster" shells (Spondylus princeps (Broderip) and the Panamanian Pearly oyster Pinctada mazatlantica (Hanley) were traded all over the Andean region.
Spondylus princeps (Broderipii 1833)	Pinctada mazatlantica (Hanley, 1846)

The Chumash Indians of California also make shell beads from the purple olive (Olivella biplicata ) shell that they use as money. The name "Chumash" literally translates to "bead money makers". You may want to visit their web site.

Olivella biplicata (Sowerby I, 1825)

• Aztecs paid shell tributes to the Emperor Montezuma.

• Ancient Phoenician coins distributed throughout the Mediterranean world were sculptured in the likeness of the scallop, murex and Triton (Charonia) shells.

Coins from many countries display a mollusc on one side.  Some examples are:
Sacred chank (Turbinella pyrum Linne), on the chertrum coin of Bhutan	Looking for photo	Turbinella pyrum
Imperial Volute (Cymbiola imperialis Linne) on the 1 sentimo Philippine coin (1983-1993)		Cymbiola imperialis
Triton's Trumpet (Charonia tritonis Linne), on the 2 vatu Vanuatu coin		Charonia tritonis
Spider Conch (Lambis), on the 1 cent Tuvalu coin		Lambis lambis
RatCowrie (Cypraea stercoraria Linne), on the 1 cedi Ghana coin		Cypraea stercoraria
Queen Conch (Strombus gigas Linne), on the 1 dollar Bahamas silver dollar		Strombus gigas
For more examples of coins bearing a molluscan image, please visit Guido Poppe's excellent site "Conchology.be"

Stamps from many countries feature various species of molluscs. Today there are over 5,000 stamps depicting seashells, and quite a few people collect them!

WWW Sites on Stamps bearing the molluscan image: Conchology:  by Guido Poppe:  Go to Shell Related then Stamps: "There are over 5080 stamps figured, 1600 details highlighted. You can search by country, by theme, family, species etc... Each stamps is documented (when you click on it). This database has been compiled by philatelist Tom Walker from Great Britain. He will be delighted to receive news from fellow collectors who may detect stamps not listed as yet, or just to have contact with you to discuss the many topics around this fascinating hobby." Cone Shells on Stamps: by Dr. Bruce Livett: "“Tom Walker (tom@tmwalker.co.uk) has created the following resource detailing countries where particular species of cone shells are illustrated on stamps.    This comprehensive catalogue now has illustrations of nearly every stamp. Click on the particular Country to view. Tom is always happy for new collectors to contact him."  This is one of Dr. Bruce Livett’s sites from Grimwade Laboratories. Cone Shells From Around the World Stamps:  Another great stamp page by Dr. Bruce Livett Books on Stamps bearing the molluscan image: A Checklist of Mollusks on Postage Stamps: by Tom Rice (Of Sea and Shore) Stanley Gibbons: Collect Shells on Stamps