THE ORDERS OF TELEOSTOMOUS FISHES 503 



fishes, Icosteidae or Rag-fishes, Acrotidae, Tetragonuridae or 

 Square-tails. By Gill and Jordan the first four families were 

 placed with the Scombroidea after the Bramidae or Pomfrets, 

 while the Tetragonuridae were segregated by Gill in a super- 

 family coordinate with the Scombroidea. Boulenger sinks the 

 Nomeidae and Centrolophidae in the Stromateidae, the Acrotidas 

 in the Icosteidae, and believes that the near connection of the 

 Tetragonuridae with the Stromateidae is shown by the common 

 possession of oesophageal pouches beset with papillae and gill- 

 raker-like knobs below the pseudobranchiae. Both families are 

 pelagic or deep-sea, feeding on Crustaceans, the fry of other fish , 

 or more frequently upon Medusae, under the protection of whose 

 stinging tentacles certain of them swim, as in the Caranx medusi- 

 cola among Scombroids (Boulenger). The deep-sea Icosteidae, 

 which have a flimsy cartilaginous skeleton, lack the oesophageal 

 teeth and the processes of the last gill arch, but Icosteus at least 

 has the gillraker-like knobs below the pseudobranchiae and the 

 family is conceded by all to be allied to the Stromateidae. The 

 Tetragonuridae, though unlike the cycloid Bramidae of the 

 Scombriformes in form, resemble them, according to Tate Regan, 

 in many significant details of the skeleton. 



On the other hand, they present some resemblances to the 

 Mugilidae near which they were placed by Gunther, and Boulenger 

 even places the whole group of families with the Percesoces, 

 thus removing them from all connection with the Scombriformes. 

 The group has apparently descended from some deep-bodied or 

 subcycloid forms resembling the Bramidae and probably retaining 

 the vertebral formula 10 + 14 which seems to be demanded for 

 the ancestral Acanthopterygians. This low formula is actually 

 very nearly realized in the Black Ruffs or Rudder-fishes, Centro- 

 lophus, Palinurichthys (10 + 14 or 15), the number of vertebrae 

 rising to 30-46 in the remaining Stromateidae, 58 in the Tetra- 

 gonuridae, and, finally, to as many as 70 in Acrotus of the Icos- 

 teidae (Jordan '96). In the Tetragonuridae and Stromateidae the 

 ventrals when present, have one spine and at most 5 soft rays, 

 as in Percesoces, Scombriformes, and typical Perciformes. As 

 we seem forced to rely on rather trivial but possibly significant 

 characters, the group may be distinguished from the Percesoces 



