| Summary: | The Miocene long-snouted dolphin species Eurhinodelphis cristatus ( sensu ABEL, 1902) (Cetacea, Odontoceti, Eurhinodelphinidae), recognized in the area of Antwerp (North of Belgium, southern margin of the North Sea Basin) and the east coast of the USA (Maryland and Virginia), is re-described, including several undescribed specimens associated with ear bones and teeth. The systematic affinities of this species with other members of the family Eurhinodelphinidae are investigated, leading to its inclusion in the new genus Xiphiacetus , together with the species Eurhinodelphis bossi ( sensu KELLOGG, 1925). The asymmetry of the skull is discussed, especially for a strange specimen with an asymmetrical basicranium interpreted as the consequence of pathology. Thanks to recently found specimens, the stratigraphic range of Xiphiacetus cristatus might be extended in the Upper Miocene, widening the Eurhinodelphinidae distribution, previously limited to an Upper Oligocene - Middle Miocene interval.The description in X. cristatus of several structures related to the telescoping of the skull, hearing, and the feeding apparatus, considered as derived compared to other eurhinodelphinids, allows suggestions concerning evolutionary trends inside the family.A cladistic analysis is undertaken in a way to examine the phylogenetic relationships between the best-known eurhinodelphinid genera. The main results of the analysis are a sister-group relationship between Schizodelphis + Xiphiacetus and Ziphiodelphis + ( Mycteriacetus + Argyrocetus ), and a more stemward Eurhinodelphis . This topology leads to some hypotheses concerning the evolution of the habitat of the eurhinodelphinids. An appendix contains remarks about the systematic status of several taxa usually included in, or related to, the family Eurhinodelphinidae.
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