Shell depressed, with three flattened, rapidly expanding whorls, which have a tendency, in old individuals, to overhang the suture anterior to them. The upper surface is traversed by numerous slender, slightly elevated, revolving threads, which are crossed by faint lines of growth. Outer edge of whorls subcarinate. The basal surface is less flattened, but similarly sculptured, except that the very wide and funnel-shaped umbilicus is destitute of revolving striae, and the lines of growth are here a little stronger. Aperture excessively oblique, with the anterior angle much produced ; lips hardly thickened, and but slightly interrupted at the junction with the body whorl. Nacre, salmon-color; external surface pinkish white, brilliantly pearly where eroded. Lat. of largest specimen, 0.85 inch; alt., 0.5 inch; defl. 88°.

This species is more flattened than any species except M. helicina, which it somewhat resembles in form, though more carinated, and otherwise widely differing in character. It is not allied to any West American species known to me, though it may have relations in some Japanese form. It is a thin and light shell.

Alaska, USA. Iliuliuk Harbor, Captain's Bay, Unalashka; and larger specimens in the Akutan Pass, from ten to sixty fathoms, on stony bottom. Not found in the Shumagins.