After speaking to friends and singers alike, I have decided to amend my proposed nomenclature for those women who sing in the bass tessitura.
Previously I proposed the name Oktavistka, a femine form of the Russian term Oktavist.
I now think that it would be easier to use and understand the term Contralto Basso.
I think it sounds and feels lower than the Contralto Profondo, my name for the female tenor, and is easier to recognise as part of the current Fach system.
To recap, I propose the term Contralto Profondo for female tenor, and Contralto Basso for female bass.
All the best,