Ptychobela vexillum is a species of sea snail, a marine gastropod mollusk in the family Pseudomelatomidae, the turrids and allies.
R.N. Kilburn proposed in 1989 Brachytoma vexillum <small>Habe & Kosuge, 1966</small> as a synonym of Ptychobela suturalis <small>(Gray, 1838)</small>
The epithet vexillium was probably a misspelling in the original text, but was not indicated as such. Therefore, it takes priority over vexillum, published five-month later and repeated later by some authors.
The length of the shell attains 46.5 mm, its diameter 14.5 mm.
This marine species occurs in the South China Sea, off the Philippines and Japan; also off Australia (Northern Territory, Queensland, Western Australia).