Total guess but the shape fits as well as the ridges and the rust colour - got the idea from http://www.mollusca.co.nz/speciesdetail.php?speciesid=2488&species=Dosina%20mactracea
Total guess but the shape fits as well as the ridges and the rust colour - got the idea from http://www.mollusca.co.nz/speciesdetail.php?speciesid=2488&species=Dosina%20mactracea