Perrierina insulana

In the original description, Powell described the species as follows:

Shell minute, thin and fragile, ovate, equivalve and inequilateral. Beaks fairly prominent, with a moderately large rounded prodissoconch which is marked off from the post-embryonic part of the shell by a slightly raised thin rim. Sculpture of exceedingly fine and closely spaced concentric growth striae. Under a low power lens the surface appears to be smooth and glossy. Hinge plate narrow and long, typical. Right valve with two divergent cardinals, which are situated in front of the narrow oblique resilium. In addition there are four anterior and five posterior lamellae set obliquely on the distal parts of the hinge-plate. Left valve with three anterior cardinals, and the corresponding lamellae. Central cardinal rectangular, outer two narrow and slightly divergent. Valve margins smooth except for a few weak crenulations on the posterior section of the ventral edge. Colour creamy buff tinged with light brown towards the beaks. The hinge plate and provisions are stained reddish-brown, and there is a faint open pattern of a few zigzag lines, in light brown over the whole shell. The shells of the species measure 1.6 mm (0.063 in) in height, 1.9 mm (0.075 in) in width, and a single valve has a thickness of 0.4 mm (0.016 in). It can be distinguished from P. …

P. insulana is endemic to New Zealand, found in the waters of the Chatham Islands and Stewart Island at depths of between 0–55 m (0–180 ft). Previously, the species was thought to be endemic to the Chatham Islands.