The diagnosis follows Mertens (1956). Historically, Bairdoppilata pseudoseptentrionalis Mertens, 1956 has been mistaken for B. subdeltoidea (Mnster, 1830), as the former species has never been adequately illustrated since its description by Mnster (1830). Several sub-species were added to Bairdoppilata subdeltoidea during the 19th century, which increases the difficulties in establishing its current taxonomic status. The most recent review of the species is in Deroo (1956), who renamed it as Bairdoppilata roemeri, with a lower CretaceousTertiary stratigraphic range. Assuming the species is still valid, it has to be separated from Bairdoppilata pseudoseptentrionalis, at least in terms of age; the former is considered later CretaceousTertiary (Mnster 1830), while the latter is from the late AlbianCenomanian (Mertens 1956). The specimens in Kaye (1965), Grndel (1966) and Jarvis et al. (1988) present a straighter posterior portion of the dorsal margin in the left valve, when compared to the more rounded one in B. pseudoseptentrionalis. In Keen & Siddiqui (1971) and Babinot et al. (1985b), the specimens presents a generally wider overlapping and less rounded overall shape.
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