The shell is of moderate size for the genus (maximum length 14 mm) and broadly lanceolate. The spire is high and acute, consisting of six or seven broad, strongly dorsoventrally flattened postnuclear whorls and a protoconch of undetermined nature. The suture is deeply impressed but is largely obscured by varical buttresses. The body whorl is moderately large and broadly fusoid. The aperture is small and ovate, with a barely perceptible aval sulcus. The outer apertural lip is barely erect, its inner surface smooth. The columellar lip is smooth and entirely adherent. The siphonal canal is moderately long, narrowly open, and slightly dorsally recurved.
The body whorl bears two major lateral varices and two minor varices, one of these (the left) ventral to one lateral and the other (the right) dorsal to the other lateral. The varical flange at the growing edge is strongly constricted above the canal. Spiral sculpture consists of an axially striate and spirally incised intritacalx.
Shell color is waxy white. The apertural margin is porcelaneous white, and the interior of the aperture is golden orange to apricot.
Radwin & D'Attilio, 1976

A. senex most closely resembles A. pollux, but differs from it in its proportionately larger aperture, the non-denticulate nature of the inner surface of the outer apertural lip, its adherent columellar lip, and in its less dorsaIly reflected, more angulate varical flanges.

maximum length 14 mm.

Off the southeastern coast of the United States (off Cape Lookout, North Carolina ) and the Gulf of Mexico (off western Florida).