Eight calcite layers of bivalves are examined in the view of QTA. We use the QTA information to compare calcite prisms of a fossil species, Trichite, with other outer prismatic calcite layers. The results indicate that the fossil species exhibit textures close to the ones of Ptedomorphia, but considerably different from the ones of mytilids, as expected from molecular analysis. Texture analysis results point out that inside the Pterioids, the Pectinoidea family is probably more distant than Pterioidea and Pinnoidea ones, coherently with other studies, and perhaps closer to Mytiloidea. However, texture analysis seems to favour a closer relationship of Trichites with Pinnoids than with Pteriids.