Original taxon: Trigonella subtruncata.
10-15m deep, Málaga, Andalucia, S. Spain. 23mm.
« This species [is] of a triangular shape, for the sides are much flatted, or almost truncated, and, when the shell is shut, have a strong heart-like impression. The valves very deep or concave ; and the beaks strong, pointed, turned inwards, and just overtop the commissure… » – E. M. Da Costa: Historia naturalis testaceorum Britanniae, London 1778, via BHL.
Synonyms: deltoides, euxinica, striata, triangula…
Atlantic specimen, collected in sand at Boiro, A Coruña, Galicia, NW. Spain. 22mm.
« Shell ovately subtriangular, inequilateral, transversely striately grooved, chalk-white beneath a dirty-yellowish epidermis, anterior side rounded, posterior slightly beaked, longer ; area and lunule rather large, striated ; ligament conspicuous without ; umboes approximated. » – L. A. Reeve: Conchologia iconica vol. VIII, London 1855, via BHL.
Beachstormed specimen, Fano, Puglia, S. Italy. 17,5-21mm.
« Mactra subtruncata: decidedly inequilateral, triangular or trigonally ovate ; surface partially covered with regular concentric grooves ; posterior end more or less acutely angulated below. Umbones prominent. Dorsal areas and lateral teeth sulcated. » – Forbes & Hanley: A history of British Mollusca and their shells vol. I, London 1853, via BHL.