Diloma bicanaliculatum, common name the knobbed top shell, is a species of small sea snail, a marine gastropod mollusk, in the family Trochidae, the top snails.

This marine shell is endemic to New Zealand and occurs off North Island, South Island and Stewart Island.

A subspecies, Diloma bicanaliculata Lenoir, was once used for specimens between Cook Strait and Stewart Island.

[3] The subspecies is not listed on the World Register of Marine Species, so it may no longer be valid.

This Trochidae-related article is a stub.