Shell ovate, flattened, membranaceous, pellucid, with concentric bands of brown and greenish-white. The whole surface is sculptured by exceedingly fine, close, subequidistant radiate striae, cut up into minute oval nodules by growth-lines. Colour dark brown, lighter near the apex, banded with narrow white or light-green concentric lines. Apex anterior, submarginal, exactly in the middle line, sharply pointed, and directed forward. Inside with an emerald ring around the muscle-impression, margin sharp, with a brown border ; central area showing the concentric bands of the dorsal part of the shell, and having an elongated patch of light emerald in the centre. Length, 15 mm. ; breadth, 12 mm. ; height, 2 mm.

Slipper Island, Coromandel Peninsula, North Island, New Zealand, 10.4mm., 1952.
The « Blue-Ringed Limpet » must be one of the most striking of all lottids. The shell is characterised by a pattern consisting of radial green to brown lines with the interline spacing filled by a brilliant turquoise or blue. A algae-grazing gastropod, it inhabits rocky surfaces of intertidal to very shallow water less than -10m deep and is endemic to the North, South, and Stewart islands of New Zealand. Although locally not uncommon, it is somewhat rarely seen on the shell market probably due to its small size and difficulty in obtaining quality specimens as the shell is extremely fragile as the specific epithet suggests. Typical shell length around 15mm. and very large specimens may exceed 20mm. It can only be confused with its only congener Atalacmea multilinea Powell, 1934 endemic to the South Island of New Zealand, which has a similar pattern but with interline spaces filled by off-white to light brown instead of torquoise; the greenish lines are also generally thinner. A. multilinea is also much smaller than A. fragilis, averaging at about 7mm. and maxes out around 12mm.

Throughout New Zealand and at the Chatham Islands, under stones between tide-marks.