Nemocardium was named by Meek (1876) [Sepkoski's age data: K Apti-l R Sepkoski's reference number: 1112]. It is extant.

It was reranked as Protocardia (Nemocardium) by Woodring (1925); it was reranked as Cardium (Nemocardium) by Vredenburg (1928).

It was assigned to Protocardia by Woodring (1925); to Cardium by Vredenburg (1928); to Protocardiinae by Moore (1976), Vokes (1980), Woodring (1982), Dockery (1982), Squires (1984) and Squires (1987); to Laevicardiinae by Schneider (1995) and Coan et al. (2000); to Veneroida by Sepkoski (2002); to Cardiidae by Turner (1938), Durham (1944), Moore (1984), Squires (1988), Squires and Demetrion (1992), Lamprell and Whitehead (1992), Squires (1999) and Schneider (2002); and to Fraginae by Moore (2003).