1995 年 1 巻 1 号 p. 11-22
The variation of concentrations of elements with growth in the calcitic outer shell layer of Mizuhopecten yessoensis (Jay), living in Mutsu Bay, northernJapanwas for the first time presentedin detail.The variation was clarifiedfor the contentsof elevenelements： Li, Na, K, Mg,Sr, Ba, Fe, Mn, Al,B and P. The variation patterns make to divide the elements into the following four groups： (1) magnesium, strontium, barium, iron and manganese； showing the seasonal variation pattern. These are occupied in the lattice sites in the calcium carbonte's crystal. (2) lithium and sodium; showing the seasonal variation, pattern with reverse pattern for the former group. These are associated with inclusions and/or organic matrices. (3) aluminium, pottasium and phosphorous； showing a random variation pattern. These are originated from foreign detrital grains. (4) boron； showing no seasonal variation pattern and partially high content Boron may be exsited as an other phase with small garains. The difference among these variation patterns originates in the difference of phase within shell. The variations of the firstand secondgroupscan beexplained by ”optimum condition model” proposed herein.