Prehistoric sites in the coastal regions of Japan are usually accompanied by large shellmounds. Among the many types of food remains found in these mounds, the molluscan shell is the most prominent and thus is regarded as having been one of the main foods for the Jomon people in these coastal sites. Fortunately for prehistorians, the shells excavated from the shell middens are well preserved, providing useful dietary data (Sakazume, 1960) and environmental information for reconstructing the shore line during the Jomon transgression (Tonogi, 1938; Esaka, 1954).

The seasonal patterns of exploitation by hunter-gatherers have recently become one of the main concerns of prehistorians interested in reconstructing prehistoric economic life (Coutts and Higham, 1971). Shellfish are generally available throughout the year and could have been an important food resource for prehistoric people, especially during shortages of other foods (Cook, 1946; Meigham et al., 1958a & b; Evans, 1969; Voigt, 1977). Hence, shell-gathering intensity might be influenced by other exploitative activities. Also, shellfish are easily collected during the spring equinox tide, and seasonality might be influenced by this ecological factor.

However, for prehistorians intent on reconstructing shell-collecting activities, the first and most difficult barrier is the estimation of the intensity of the activity (Bailey, 1975). Study of the shell collection season provides important information not only on the seasonality but also on the intensity of the shell-collecting activity; the distribution of seasonally dated clams in a shell layer gives pertinent information to infer the speed of accumulation of the shell layer.

Many methods have been used for estimating the season of the shell-collecting activities of prehistoric people. Weide (1969) and Ham and Irvine (1975) used the winter band observed on the shell surface. For the estimation of sea-water temperature at the time of shell collection, Shackleton (1973) measured the ¹⁸O/¹⁶O ratio of samples taken from the shell margin of Patella. Coutts (1975) read the growth lines in Chione stutchburyi excavated from southern New Zealand.

Basic research on seasonal dating by counting growth lines is discussed in Part I of this paper, using the clam, Meretrix lusoria (Röding), which is widely distributed along the coasts and also commonly found in the prehistoric shellmounds in Japan. In Part II, the results of seasonal dating analyses of more than 300 block samples collected from shell deposits in 12 archaeological sites in the south Kanto district are described. These samples span the time from the Jomon period to the Edo period (6000-300 years B.P.).

This paper is the doctoral dissertation submitted to Faculty of Science, The University of Tokyo in 1979.