The status of Calopteryx okinawana Matsumura, 1931 (Zygoptera: Calopterygidae)

In his “ 6000 illustrated insects of Japan-Empire", S. MATSUMURA (1931, p. 1454) described and illustrated Calopteryx okinawana Mats, as a new species from Okinawa, Japan. This is conspecific with Matrona basilaris japonica Foerster, 1897. However, as far as I know, this synonymy has not been presented in any publication. Consequently, in their catalogues, C.A. BRIDGES (1994) and H. STEINMANN (1997) list okinawana as a good species in Calopteryx, though the former hesitantly so, with a question mark after the genus name.