Addisonia excentrica is a species of sea snail, a marine gastropod mollusk in the family Addisoniidae.

The apex presents an appearance as if an embryonic tip (perhaps spiral) had fallen and been replaced by a peculiarly blunt ovate apex, which in the young shell is nearly marginal, posterior and to the left of the middle line, but in the adult is considerably within the margin, curved downward and backward and much more asymmetrical.

The sculpture of the shell shows faint grooves radiating from the (smooth) apex and reticulated by the stronger concentric lines of growth, beside which the extremely inflated arch of the back is somewhat obscurely concentrically waved.

The scar of the pedal muscle is narrow and at a considerable distance within the margin.

These ends are connected by a line broadly arched forward and marking the attachments of the mantle to the shell over the head.