This paper explores working hypotheses concerning factors affecting the selection of Saxidomus nuttalli and Tresus nuttalli clam shell for use at inland shell midden sites where disc beads were manufactured. The particular site in question is a prehistoric archaeological site, Son-159, located in Sonoma County in the Santa Rosa Valley, about 15 miles inland. The site is near the ethnographic boundary between speakers of Southern Pomo, to the north, and Coast Miwok, to the south.