A new monotypic genus of Neogene odontocete (Isoninia borealis) is named on thebasis of a partial skull (CMM-V-4061). The holotype was found on theriverbed of the Meherrin River (North Carolina, USA) and probablyoriginated from the Miocene marine Eastover Formation. Deep interdigitationof the cranial sutures indicates that this individual was mature. The newtaxon differs from all other delphinidans in the unique combination of thefollowing characters: anteriorly retracted premaxillae and maxillae;premaxillae not contacting nasals; thick nasals with ventrolateral marginsdeeply imbedded within corresponding troughs in the frontals (this is anapomorphy); nasals with transversely convex dorsal surface; nearlysymmetrical vertex; os suturarum (or interparietal or extra folds of thefrontals) at the vertex; large dorsal infraorbital foramen level with theposterior margin of the external bony nares; and a postorbital recess on theventrolateral face of the frontal below and behind the postorbital processof the frontal. This odontocete exhibits two small but pronouncedconcavities on the cerebral face of the frontal/presphenoid that arepresumed to have held vestigial olfactory bulbs in life. Inioidea is onlydiagnosed by a single unequivocal synapomorphy: width across nasals andnares subequal. Isoninia shares this feature with other inioids and forms the basisfor the placement of Isoninia within this clade. A relatively high vertex coupledwith a supraoccipital that is deeply wedged between the frontals suggestsplacement of this new inioid species within the family Iniidae. This is thesecond inioid described from the Eastover Formation (the other beingMeherrinia isoni). This new species adds new cranial morphology and a new combination ofcranial characters to this taxonomically small but growing group of mostlymarine and mostly Western Hemisphere odontocetes (urn:lsid:zoobank.org:pub:E8B817CA-B250-42B3-9365-36EFBFE351C9).