Aucella

Aucella, genus of clams characteristically found as fossils in marine rocks of the Jurassic Period (between about 176 million and 146 million years old). The shell has a distinctive teardrop shape and is ornamented with a concentric pattern of ribs; the apex of one valve (shell half) is often curved over the other. A distinctive and commonly found Jurassic species is Aucella piochii.