Akromystax tilmachiton, gen. et sp. nov., is described from Late Cretaceous Cenomanian beds in the Lebanon. The new taxon is the first new pycnodont to be published from the recently discovered locality of en Nammoura. It is a member of the Pycnodontidae that presents an unexpected combination of primitive and derived characters, including autapomorphies such as: hypertrophy of the lateral laminae of the mesethmoid, covering the lateral portion of the ethmoidal region plus part of the lower jaw; extrascapular bone forming part of the border of the orbit; expansion of the premaxilla, which bears no less than eight molariform teeth arranged in at least two rows; opercular and preopercular bones separated from each other; unique pattern of scale ossification; overlapping of the spines of the ventral keel scales; first ventral keel scale markedly larger than other keel scales. A new type of replacement teeth is reported for the first time in a pycnodontiform fish. Akromystax tilmachiton is at present the most primitive taxon of the family Pycnodontidae, despite its relatively derived characters, and confirms the mosaic evolution of the pycnodonts. The new taxon is present in the localities of Haqel, Early Cenomanian, and en Nammoura, Middle Cenomanian. It is an interesting common element of both localities, indicating that their paleoichthyofaunas, contrary to previous thought, are more similar than other components of their fossil associations.