Fossil bivalve shells are well-suited for landmark/semilandmark morphometric analysis because they preserve both traces of the internal anatomy and the whole shell outline. Utilizing landmarks and semilandmarks, we have characterized internal and external shape variation in a monophyletic clade of Cenozoic New Zealand and Australian crassatellid bivalves, to test the contiguity in morphospace of species-level taxa and to quantitatively examine the “Concept of Independent Entities” of Yonge (1953). Thirteen species from two genera (SpissatellaFinlay 1926 and EucrassatellaIredale 1924) are investigated. Spissatella n. sp. C is confirmed as forming a contiguous group separate to S. trailli and S. clifdenensis. Shell outline and internal anatomy are found to covary in shape, refuting the “Concept of Independent Entities” in the study group.