This is a subspecies from Hawaii with adults always smaller than the adult nominate species. The spiral cords are divided into two cords making the nodes caused by axial riblets much more narrow. Of¬ten there are narrow spiral cords on the divided cords. Cernohorsky has shown that the radulae of this subspecies differs from the radulae of the nominate species in having fewer denticles on the lateral rachidian. The animal is quite similar to that of the nominate species though the brown on the foot and siphon is lighter. W/L of illustrated specimens were 0.33 to 0.37 and S/L was 0.49 to 0.50.
Cernohorsky (1991) page 105 to 106 treats Mitra emersoni Pilsbry, 1921 as a synonym of N. clathrus rather than as a subspecies as we have treated it. As a geographically isolated form, we consider it a subspecies. Cernohorsky (1991) page 105, fig 100-2 and 100-3 illustrates this subspecies as the holo-type of M emersoni Pilsbry, 1921 held in the Academy of Natural Sciences, Philadelphia as specimen no. 46804.