The differences with Pholadomyidae ae mainly anatomical. E. V. Coan indicates a morphological feature: the pallial sinus is smaller than in the members of the latter (Malacologia vol.42, 2000).
 

« Valves almost equal, slightly truncated anteriorly; the longitudinal ribs are very obscure; umbones small. » – Melvill & Standen: “Report on the Marine Mollusca obtained during the First Expedition of Prof. A. C. Haddon to the Torres Straits, in 1888-89”, Journal of the Linnean Society of London, Zoology vol.27(174), London 1899, p.202 in fam. Pholadomyidae.