The dental morphology of the pycnodontid fish †Stemmatodus rhombus (Agassiz, 1844) from the Lower Cretaceous (lower Barremian) of southern Italy is described in detail. SEM pictures of vomerine and prearticular teeth are provided for the first time allowing the comparison with other Early Cretaceous pycnodonts, which are only known from isolated dental remains. The dentition of †Stemmatodus rhombus consists of incisiform grasping teeth on the paired premaxillae and dentaries and crushing teeth on the unpaired vomer and paired prearticulars. The vomerine teeth are arranged in five longitudinal rows, which display symmetry with a distinct median principal and two lateral rows. The prearticular bears three longitudinal rows. Teeth of the main row are much wider than those of the lateral ones. The tooth crowns are rather flat and expose a shallow apical depression, which is surrounded by a ring of widely-spaced small tubercles. The ornamentation and arrangement of teeth distinguishes dentitions of †Stemmatodus from all other pycnodonts. The wear pattern of the teeth is evaluated and the significance of the dental morphology in pycnodont taxonomy is discussed. In addition, the systematic position of †Stemmatodus is discussed.