It needs scarcely be said that a biometrical approach on the basis of sound population concept is one of the most reliable methods for the taxonomic discrimination and the consideration of phylogeny in palaeontology as well as in neontology. As a theme of the palaeontological exercise for students in the academic year 1967, we attempted to examine the variation and relative growth of several Recent bivalves on the basis of a thanatocoenosis of shells at the coast of Tsuyazaki, about 22 km north of Fukuoka City (Text-fig. 1). The result of this exercise on the left valves of two species of Glycymeris, which was confirmed again by the first author, is summarized here as the first report of this serial study. 1) The 26 individuals of Glycymeris vestita (DUNKER) and 113 individuals of Glycymeris albolineata (LISCHKE) from this locality seem to represent two interbreeding populations respectively, because the resulting frequency distribution concerning several quantitative characters appears to be normal in each species. The two species can be discriminated by the difference of the relative length of hinge plate, which is very significant according to the result of STUDENT's t-test. 2) PEARSON's coefficient of variation (V) may vary to some extent among characters even within one population. In the two species the inflation of valve (T/H) is more changeable than the elongation of shell (L/H) and relative length of hinge plate (D/L), although it may be more or less influenced also by the ontogenetical transformation. 3) The bivariate analyses between the measured parameters (L, H, T, D) in the two species resulted in the following simple allometrical equations which were gained by the regressions (fitted by least squares) from all the measured individuals (Text-figs.4-9). G. vestita : L=1.143H^<0.993> T=0.189H^<1.117> D=0.548L^<1.001> G. albolineata : L=0.982H^<1.037> T=0.247H^<1.057> D=0.627L^<1.013> It is worthy to note that the growth rate of T to H is much larger than 1 in the two species, indicating a distinct positive allometry. As to other bivariate relations the growth had better be said nearly isometrical. 4) An indistinct critical point, where the growth rate may be changed a little, seems to be shown in each double logarithmic graph between L and H and also between T and H in G. albolineata (Text-figs.7, 8). 5) In G. albolineata a distinct critical point is recognized by the double logarithmic graph which shows the relative growth between the weight of shell (W) and the volume of circumscribed cuboid (LHT)(Text-fig.10). The allometrical equation is W=0.405(LHT)^<0.982> for the smaller specimens and W=0.041(LHT)^<1.487> for the larger specimens. This fact certainly indicates that the relative thickness of test becomes larger after the beginning of the gerontic stage. Such a bivariate analysis, therefore, may be generally applicable as a useful method to determine whether or not a collected fossil population includes gerontic individuals.

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This study is made in order to examine the relation between the morphological structure types ofshell tissues redescribed by the author and the histological nature of those organic matrices in some species of the bivalve molluscs. The sections of decalcified matrices including eight structure types are ready for microscopic observations. They are dyed by hematoxylin-eosin, Azan, Van Gieson, VERFOEFF's stains and some stains for protein and polysaccharid reactions. The result of staining is described in each type and shown in the Table 2. It is concluded from these data as follows. Organic matrices in shell tissues of various species made of the same structural type possess nearly similar histological natures. The shell tissue of each type is made of organic matrices having the characteristic staining ability and morphological features. But we can recognize some different types having similar natures of organic matrices one another, for example, in crossed lamellar and complex structures. The difference of structure types is related to that of the organic matrix rather than that of the inorganic substance.

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