 "Mesacanthus" have pectoral, pelvic, anal and dorsal fin spines, as well as a pair of prepelvics (intermediate spines between the pectoral and pelvic fin spines) and small, unornamented, diamond shaped scales.According to Agassiz, the genus also has a distinct tail in which the upper lobe extends to a sharp point and the lower lobe forms a small triangle.Overall the genus is small (average length = 30mm) and fairly conservative for acanthodians.