Can anybody please help with identification?

[mikede]

From Brazil: it is a species of the genus Anadara (family Arcidae). You can check this site, which pictures all brasilian Arcidae: <a href="http://www.conchasbrasil.org.br/english/conchology/especies.asp?idfamily=55" target="_blank"><!-- m --><a class="postlink" href="http://www.conchasbrasil.org.br/english/conchology/especies.asp?idfamily=55">http://www.conchasbrasil.org.br/english ... dfamily=55</a><!-- m --></a> . There you should be able to identify your shell more exactly.

From Portugal: seems to be a Spisula solida.