Symmius Richardson, 1904: 39 -40; Nordenstam, 1933: 103; Poore, 1984; 76. Type species. Symmius caudatus Richardson, 1904.
Other species. S. planus Nunomura, 1984, S. philippinensis Poore, 1991.
Remarks. Richardon (1904) established the genus for the new species S. caudatus from off Osezaki, Izu Peninsula, Japan, from a depth of 109– 127 m. Poore (1984) redefined the genus with the redescription of the type species. A second species, S. planus was described by Nunomura (1984) from the Otsuchi Bay, Japan, from a depth of 4–10 m depth. A third species, S. philippinensis was described by Poore (1991) from Philippines, from a depth of 130– 137 m. The genus has a North West Pacific distribution.