A medium-sized species of Squalus of the ‘highfin megalops group’ is characterized by the following combination of characters: snout relatively short; first dorsal fin tall and upright, upper posterior margin almost straight; caudal fin with broad white posterior margin, no dark caudal bar; flank denticles tricuspid. These characters clearly differentiate this species from the three other sympatric Squalus species. Squalus formosus is morphologically closest to S. albifrons from eastern Australia but differs in the following characters: first dorsal fin with a distinct, broad white anterior margin (v. no distinct white marking); second dorsal fin height 5.7–6.4 v. 4.3–5.1% LT; first dorsal fin height 9.0–10.5 v. 7.7–8.9% LT, anterior margin 12.4–14.6 v. 10.9–12.7% LT; eye slightly larger 4.8–5.3 v. 4.4–4.8% LT. Squalus formosus can be further distinguished from other Squalus species in the following combination of characters: pre-second dorsal length 3.7–4.4 times pectoral-fin anterior margin; preoral length 2.2–2.3 times horizontal prenarial length; head length 4.0–4.7 times eye length; interorbital width 1.4–1.6 times horizontal preorbital length; posterior margin of second dorsal fin deeply concave; second dorsal-fin spine with a broad base; dorsal surface of head dark, sharply demarcated from paler ventral surface; 45–46 monospondylous centra, 94–95 precaudal centra, 123–124 total centra; adult maximum size at least 73 cm LT (Ref. 87791).