Hirundichthys is a genus of flying fish. They have elongated, moderately thick, ventrally flattened bodies. The pectoral branch of the lateral line is absent. The upper jaw is not protrusible. The dorsal fin has fewer or equal rays than the anal fin; the dorsal fin is low, with the anterior rays the longest, the pectoral fins are strikingly long, reaching to or almost to caudal fin base; pelvic fins are long, reaching beyond the anal fin origin, and their insertion is closer to the anal fin origin than to the pectoral fin insertion.