抄録
28 twin point groups of ordinary twins are assigned to the respective crystal systems of twinning, using the notations of Hermann-Mauguin and Schönflies.
Ordinary twins are classified into six types by the kind and number of the twining planes; namely, A. Interpenetration, B. Double cross twin, E. Biaxial cyclic contact twin, and F. Biaxial contact twin. The first four types are collectively called thepenetration twin, and the last two the contact twin.
