Lewis & Short

sēpĭa, ae, f., = σηπία, the cuttle-fish, having a black, inky liquid, Cic. N. D. 2, 50, 127; Plin. 9, 29, 45, § 84; Plaut. Rud. 3, 2, 45; Col. 6, 17, 7.
This liquid was used for ink, Pers. 3, 13; hence, transf., ink: furva, Aus. Ep. 4, 76.