Diagnosis. Shell large, white, with coarse radial ribs. Apex nearly central; selenizone marked by interior channel and arched exteriorly. Juvenile shells finely punctate and deeply notched, apex close to posterior edge of shell.
Remarks. Scelidotoma differs from other emarginuline genera in undergoing an ontogenetic change— the juvenile shells are deeply notched as in Emarginula, the notch becoming sinuous and marginal in mature shells.
I had previouly thought that the genus Arginula Palmer, 1937, type species Emarginula arata Conrad, 1833, from the Eocene of Alabama, was appropriate for the species bella, as used by Kozloff (1987:200), but no longer hold that view.
There are two species in the northwestern Pacific: Scelidotoma gigas (Von Martens, 1881), and S. vadosinuata (Yokoyama, 1922).