TRIGONIA


Meaning of TRIGONIA in English

genus of mollusks that first appeared during the Jurassic period, which began about 208 million years ago. The still-extant Trigonia has a triangular shell with distinctive concentric ridges on its surface as well as nodular outgrowths. A different ornamental pattern is present in the posterior parts of the shell.

Britannica English vocabulary.      Английский словарь Британика.