Shell small, biconical, white; protoconch globose, smooth, of one and a half whorls. Teleoconch of 4,5 very slightly convex whorls. Sculpture of low axial ribs (about 15 on the penultimate and last whorl), slightly opisthocline, and of very flat spiral cords, much broader than their interspaces (three on first teleoconch whorl, five on penultimate, 17 on last whorl). Under high magnification, whole surface bearing axial wrinkles parallel to the growth lines. Suture shallow. Aperture narrow, outer lip with 4 denticles inside, the adapical one strongest, thickened outside; inner lip plain, with two strong folds near its middle, the adapical one the largest. Dimension of the holotype: 6.4 mm height x 2.8 mm diameter. ETYMOLOGY. — From the Latin name of a white, marble like stone, alluding to the colourless shell; used as a noun in apposition.

There are two other described species from the Atlantic with a similar cancellate sculpture. Mitromorpha biplicata Dall, 1889 has one more teleoconch whorl (5-6 instead of about 4,5) at roughly the same size (7 mm). The sculpture is also different, being raised spiral cords separated by broad interspaces, in which additional cordlets appear at the end of the last whorl, whereas in M. alabaster n. sp. the spiral cords are flat and much broader than the interspaces. Mitromorpha dalli Dautzenberg & H. Fischer, 1896, is twice as large with a similar sized protoconch, which results in a profile with a very much more pointed apex. The latter is so far only known from the holotype (figured in Bouchet & Waren 1980), collected off the Azores at a depth of 1300 m.

TYPE LOCALITY. — Off W Gran Canada, 28°08.32'N, 15o51.94'W/28°08.5rN, 15°51.6l'W, 480 m.