Lethenia
Lethenia is an extinct genus of mackerel shark from the Eocene and Oligocene epochs. It contains two species; the type species L. vanderbroecki is from the early Oligocene of Belgium, while L. carranzaensis is from the late Eocene to early Oligocene of Chile. It is considered closely related to Isurolamna and sometimes included within it. It differs in the morphology of its teeth, which are much more gracile than Isurolamna and has larger spacing between its crown and lateral cusps.