Protarpon priscus was a large elopid relative represented by substantial three-dimensional skulls in the London Clay. Its elongate head and large opercular region indicate a sizeable active swimmer. By comparison with living elopiforms, capture of smaller fishes and mobile invertebrates is a reasonable ecological interpretation, although direct dietary evidence is absent.

The skull roof carries paired raised ridges that diverge posteriorly, giving the cranium a distinctive architecture. Better-preserved examples retain enough of the cheek and opercular series to show that this was a large-bodied fish rather than merely a small skull morphotype.