In some specimens the umbilicus is entirely closed and in others it is a mere slit. The young of M. frigidus have a more open umbilicus than larger specimens and hence may be difficult to distinguish from the young of M. vahli of similar size. The similarity is especially marked if they are in alcohol or other fluid, for then the delicate, incised lines on the base near the umbilicus of M. frigidus are often invisible. However, if the shells are allowed to dry, M. vahli remains as glossy as ever and M. frigidus becomes duller, with a silky rather than a glossy surface.

The range of M. frigidus is from approximately long. 134° to 170° W. and lat. 57° to 71° N., or from the Admiralty Islands (near Juneau), Alaska, to Nunivak Island, Bering Sea, and north and east to Point Barrow, The latter is a new locality. In several publications the type locality of M. frigidus is given as "north of Bering Strait." The type specimen is from the north end of Nunivak Island, which is 5° south of Bering Strait.