Standards have been empirically developed to describe various morphological characters of eurypterids. The standards pertain to the following characters: 1) shape of the prosoma; 2) shape of the metastoma; 3) shape of the eyes; 4) position of the eyes; 5) types of prosomal appendages; 6) types of swimming leg paddles; 7) structure of the doublure; 8) differentiation of the opisthosoma; 9) structure of the genital appendages; 10) shape of the telson; and 11) types of ornamentation.