Palaeocybium proosti is a very rare fish from the London Clay, represented by only one partial skull in the Natural History Museum, London and only a few partials in private collections. It is however possible to find isolated teeth on the beach of the Isle of Sheppey.

The teeth of Palaeocybium are the most distinctive feature. There is an outer row of minute, laterally flattened, blunt-tipped teeth and then an inner row of tightly packed, significantly larger,  laterally-flattened teeth which are similar to that seen in modern Barracuda fish. 

The skull represented here is that of a modern Barracuda (Sphyraena barracuda) which showcases very similar teeth morphology.