This monster is a dragon with bird’s wings and a head at either end – rather like the “pushme-pullyu” of the Dr. Dolittle stories. The name comes from the Greek (amphis, bainein, “to go both ways”): in classic Greek myth, it’s a serpent with a head at either end. Bossewell, 1572 [II.63] describes the amphisbaena but gives no picture; Brooke-Little [Her.Alph 33] has shown it was never actually used in mundane armory.
The amphisbaena used in Society armory seems to be a conflation of two forms of amphisbaena from medieval bestiaries: one with wings and two feet (as in the Aberdeen Bestiary, c.1200) and one with four feet but no wings (as in the Bestiary in the Netherlands National Library, c.1350). There doesn’t seem to be a default posture; the illustration shows an amphisbaena statant.
Edward the Gentle bears: Argent, an amphisbaena statant respectant vert, winged Or, gorged of two oak wreaths Or connected between the wings by a chain containing three Catherine wheels sable, in base a point pointed gules.
Ricola of Fenhop bears: Or, an amphisbaena passant gules within a bordure gules bezanty.
Solveig Langlif bears: Per pale purpure and Or, an amphisbaena, heads reguardant, between three crescents counterchanged.