Shell ovate but varying with the nature of the surface to which it was attached. Compared with costata the new species has the beak narrow and strongly projecting irrespective of shell shape. The surface is neither smooth nor radially costate, but irregularly malleated. Eight obsolete radial costae are just discernible, they merely break the contour of the surface into slight planes that may be seen by rotating the shell. A juvenile has definite low weak radials, but they are not sufficiently strong to indent the margin. Most likely the malleations are reflex to the surface of attachment which is suggested as the backs of the shells of Anomia walteri. The margin is smooth and the colour buff irregularly and faintly longitudinally streaked with light brown. Interior with the septum white and grading to darker brown beneath it. The protoconch, although worn in all examples seen, is similar to that of the genotype, certainly quite unlike that of M. (Zeacrypta) monoxyla. The septum is exactly as in costata.

Length: 27 mm.; breadth, 22 mm.; height, 8·5 mm. (holotype).
Holotype in Auckland Museum.
Locality: Cape Maria van Diemen.