#monotidae

Here's a better preserved specimen.

First collected by Ferdinand von Hochstetter, and described by paleontologist KA Zittel, as Monotis richmondiana. However, later work has broken that up into 14 species and 5 genera.

Monotis species are one of the oldest macrofossils known from NZ rocks, dating back to 217 to 208.4 million years ago, but the genus was found worldwide in the Late Triassic. From the thin, delicate shell and strong byssal notch, it seems likely they lived attached to floating seaweeds at the sea surface. In New Zealand they were common enough to form fossil beds containing tens of millions of fossils.