XXII PERCESOCES 643 
Fam. 9. Stromateidae.— Although including a number of 
forms very unlike Zetragonurus in external appearance, there is no 
doubt that this family, hitherto placed near the Scombridae, is very 
closely allied to the preceding, agreeing with it in the presence 
of lateral oesophageal sacs bearing internally papillae (which are 
besides beset with setiform teeth), and, in most genera, in the 
presence of a series of knobs, more or less similar to gill-rakers, 
below the pseudobranchiae. The pelvic bones are sometimes 
free from the pectoral arch, as in the Tetragonuridae, sometimes 
more closely attached, but only by hgament, and movable. The 
principal difference resides in the scales, which are always cycloid 
and usually very small and more or less deciduous, and in the 
spinous dorsal being shorter than the soft, or even quite rudi- 
mentary. The ventrals are sometimes absent. The air-bladder is 
present or absent. The number of vertebrae varies from 24 to 46. 
Marine Fishes, pelagic or deep-sea, feeding on Crustaceans, 
Medusae, or the fry of other fish. About 45 species are known, 
referable to 10 genera: Nomeus, Cubiceps, Psenes, Seriolella, 
“Psenopsis, Centrolophus, Lirus, Stromateus, Peprilus, and Stromat- 
eoides. Many of the species have a wide distribution, but are 
rare in collections! The Black-Fish (Centrolophus niger) and 
its close ally C. britannicus, and the Rudder-Fish (Lirus pereiformis 
and ZL. medusophagus), have occurred, at rare intervals, on the 
British coasts. The Stromateidae were represented by several 
species in the Cretaceous (Patycormus and Homosoma). 
The widely distributed Nomeus gronovii, so remarkable for its 
enormous ventral fins, folding in a ventral groove, has been 
observed in New South Wales to be only found on the coast 
when the Siphonophores called “ Portuguese Men-of-War” or 
Physalia ave driven ashore, the fish swimming beneath them, as 
the young Caran are in the habit of doing under Medusae. | As 
observed by Waite,” the benefit of such a partnership must 
primarily be with the fish, for it is a voluntary agent, whereas 
the Physalia has no power of locomotion. “If the fish secures 
safety from its enemies by entering the area embraced by the 
deadly tentacles of the Physalia, which attain a length of 10 to 
1 A revision of these fishes has recently been published by C. T. Regan in Ann. 
Mag. Nat. Hist. (7) x. 1902, p. 115. 
2 Rec. Austral. Mus. iv. 1901, p. 40. Cf. also S. Garman, Bull. Labor, Univ. 
Towa, iv. 1896, p. 81. 
