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Taxonomy
Cardium (Cerastoderma) waltonianum was named by Dall (1900) [DISTRIBUTION: Early Miocene; Florida.]. Its type specimen is USNM 113819, a shell, and it is not a trace fossil.
Sister species lacking formal opinion data
C. alabamense, C. cedrelarum, C. cottaldinum, C. erinaceum, C. heinzelini, C. hernandoense, C. hispidiforme, C. knappi, C. latisulcum, C. leucostoma, C. lineolatum, C. lithopodolicum, C. problematicum, C. rouyanum, C. scabrum, C. schweinfurthi, C. transcarpaticum, C. triangulatum, C. vindobonense, C. volckmanni, C. colosseum, C. estacianum, C. sellardsi, C. triboleti, C. hanpeizanense, C. anclotense, C. brooksvillense, C. coutinhoi, C. hernandoense, C. hortensium, C. leucostomum, C. plectopleura, C. ustrix, C. viridarii, C. colosseum