xxn PERCESOCES 643 



Fam. 9. Stromateidae. Although including a number of 

 forms very unlike Tetragonurus 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 ligament, 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. 1 The Black-Fish (Centrolophus niger) and 

 its close ally C. britannicus, and the Rudder-Fish (JArus perciformis 

 and L. medusopliagus), have occurred, at rare intervals, on the 

 British coasts. The Stromateidae were represented by several 

 species in the Cretaceous (Platycormus 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 are driven ashore, the fish swimming beneath them, as 

 the young Caranx are in the habit of doing under Medusae. As 

 observed by Waite, 2 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. ffist. (7) x. 1902, p. 115. 



2 Sec. AvsfraL Mus. iv. 1901, p. 40. Cf. also S. Garman, Bull. Labor. Univ. 

 Iowa, iv. 1896, p. 81. 



