Notoacmea helmsi is a small species of sea snail or true limpet, a marine gastropod mollusc in the family Acmaeidae.
This limpet is endemic
to New Zealand
This abundant species is found in the intertidal
zone, especially in sheltered waters, attached to stones and dead shells on mud-flats.
The shell is so variable in shape and colour pattern that a precise description is difficult, and it is possible that this species may be split in due course. In general terms the shell is broadly ovate, and rather elevated, greyish-green or light brown, with 30 to 40 radiating dark lines. The interior is greenish or greyish, dark bordered, with the external radials showing through, and the the muscle attachment mark on the underside of the shell is brown, often lighter towards the centre. The radula
has the centrals long with short cusps, the laterals are short, also with small cusps, and are in two pairs near the centre of the ribbon.
The shell length is up to 11.5 mm, width 9 mm, and height 4 mm.