Are the contours of the frontal section of shell valves in Bivalvia specific?

The diagnostic importance of the character of curvature of the frontal section of shell valves in Bivalvia on the basis of determining the constant angle of the logarithmic spiral is discussed. The contours of the frontal section of shell valves in several species of mollusks of the families Margaritiferidae and Sphaeriidae have been analyzed. It is shown that in different species of the family Sphaeriidae, the values of constant angles coincide. While performing graphic constructions, it was established that the contours of the frontal section of all studied species of pearl mussels and some spheriids do not correspond to the segment of the logarithmic spiral. It was noted that the hypothesis of the species specificity of this character was not confirmed; therefore, the curvature of the frontal section of shell valves cannot be used as the main character for the systematics and species identification of bivalves.