Shell moderately large, up to 58 mm. (2,25 inches) in length, rather solid, broadly ovate, with the small erect apex nearly central; tall-conical with the sides descending almost perfectly straight; margin smooth to weakly crenulated. Sculpture consisting of weak, evenly-spaced, radial primary cords, with 3-4 secondary cords or threads in each interspace, the whole crossed by numerous concentric growth threads. Colour of exterior light bluish olive, darker towards the margin; the apex yellowish to reddish browns interior silvery bluish grey, except for the spatula, which is yellowish to orange-brown, and there is a narrow rim of greenish olive at the margin. Length: 37-58 mm; Width 32-52 mm; Height: 14,5-23 mm.

This is the furthest east yet recorded for the Indo-Pacific genus Cellana. Pilsbry (1891) considered ardosiaea to be allied to the Society Islands taitensis, but that is a most unlikely relationship. From all other species of Cellana, the Juan Fernandez shell stands apart, with its nearly circular, spreading form with its straight dorsal slopes, high conical profile, and its small, erect, nearly central apex.

Island of Juan Fernandez, off the coast of Chile.

Thiem (1917, p. 389) described in ardosiaea a presumed sensory organ, the "vorderer sub-palliater Sinnestreif" (anterior subpallial sensory-stripe), and a longer posterior one, the former evidently- the same structure as Fretter and Graham's (1962, p. 118) "lateral glandular streak" in Patella. The anterior sensory stripe, or lateral glandular streak, was noted in several species of Cellana, but not the 'posterior stripe,' which possibly, could have resulted from contraction during preservation.

Unfortunately the writer has no preserved animals of ardosiaea, but reference to Schuster (1913) and to Thiem (1917), respectively, leave no doubt that the species is a Cellana, not a Nacella (Patinigera), which latter relationship one would have expected, owing to the geographical proximity of ardosiaea to the South American mainland.
The epipodial fringe, so characteristic of Nacella and its subgenus Patinigera, is absent in ardosiaea, as also is any trace of the equally characteristic bronzy coloration of the shell.