The new endemic genus Neuquemya, from Pliensbachian deposits in west-central Argentina, is here described and tentatively referred to the Cuspidariidae on account of its shell characters. The new species Neuquemya leanzaorum has a thin, inflated shell, rounded anteriorly and rostrate posteriorly, with a narrow posterodorsal gape and opisthogyrous umbones. The hinge region bears small cardinal tubercles. The shell is ornamented by commarginal (anterior) and radial (posterior) sculpture, whereas the rostrum is smooth. The general and detailed characters of the shell are thus very similar to those of living cuspidariids. Cuspidariids are extremely specialized bivalves with special features related to their carnivorous habit. Their fossil record is scarce, and their phylogeny is poorly understood. Because a few key shell characters and all soft body features of the new genus are unavailable, the alternative possibility that his taxon could be a remarkable example of a homoeomorphic shell cannot be dismissed. If actually a cuspidariid, Neuquemya n. gen. becomes the oldest known member of the family ca. 100 Myr older than the Late Cretaceous records unequivocally accepted and supports the argument that the origin of the group is much older than its known fossil record. The possible relationships of the new genus with other poorly known Mesozoic genera are discussed. Although septibranchs in general and cuspidariids in particular are now conspicuous elements of deep-sea faunas, this new genus inhabited nearshore environments of the Neuquén Basin.
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Vol. 93 • No. 1