 "Herefordopterus" was a small-sized eurypterid with only 12 cm (5 in) in length, being surpassed in size by other pterygotioids such as "Slimonia acuminata" with 100 cm (39 in) or "Jaekelopterus rhenaniae" and (potentially) "Erettopterus grandis" with 2.5 m (8.2 ft).This size makes it the smallest genus and one of the smallest species of the entire Pterygotioidea superfamily, the related "Hughmilleria wangi" at 6 cm (3 in) being the smallest one.It had a parabolic (approximately U-shaped) to campanulate (bell-shaped) carapace (head plate) with an angular anterior margin that narrows toward the eyes, the second to fifth pair of prosomal appendages with a single pair of short spines on each podomere (leg segments) and large oval and marginal eyes.