Journal of California and Great Basin Anthropology

The study results presented in this paper are concerned only with external shell growth. In particular, this research centers on highly defined ridges and grooves on the external shell surface. These pronounced external features, or external periodic landmarks, are presumed to represent fortnightly and annual periodicities in shell growth. The presumed fortnightly ridges of Chione clams are evident as raised concentric sculptures on the shell surface, and are each supposed to represent a two-week period of shell growth. The presumed annual bands or grooves, which more often appear as checks in the shell surface, are visible on most molluscan skeletons, and are believed to record the winter cessation of growth. Biologists counting these checks achieve the chronological age of the organism. From the archaeological perspective, it has been proposed that the season of death can be inferred from the number of fortnightly ridges per year, and from the position of the last annual band in relation to preceding annuli or to the shell margin itself (Fig. 1). This paper reports the final results of a test for three seasonality methods (Cerreto 1988).