Attheya longicornis vs A septentrionalis

Hi
Has anyone the literature for distinguishing A. longicornis and A. septentrionalis?
In Throndsen, Hasle and Tangen "Phytoplankton och Norwegian coastal waters" they distinguish it by the ratio between apical-axis and length of horns.
But in this database we cite another source using a different character.
I append this species, which I presume is Attheya longicornis before publishing to the database.

b.r
Fredrik