678 TELEOSTEI CHAP. 



inserted low down. A single genus, Rhachicentrum (Ulacate), 

 with a single species from the coasts of the tropical and 

 warmer parts of the Atlantic and of the Indian Ocean. 



Fam. 3. Scombridae. Praemaxillaries large, not protractile, 

 beak-like. Vertebrae 30 to 50, without transverse processes, 

 but some of the hinder praecaudals with haemal arches ; ribs 

 inserted 011 the centra or on the haemal arches \vhen these are 

 present ; epipleurals all on the centra. Scales cycloid and usually 

 very small (except in Gastrochismci), sometimes absent. A 

 spinous dorsal fin formed of slender spines, folding into a sheath ; 

 soft dorsal longer and broken up into finlets, similar to the anal; 

 pectoral inserted high up the sides. Hypural bones completely 

 embraced by the forked bases of the caudal rays. Pseudo- 

 branchiae present. 



FIG. 415. Tunny (Thunnus thynnus). (After Cuvier and Valenciennes.) x |. 



About 5 species, referred to the following genera. : Scomber, 

 Auxis, Thunnus, Sarda, Cylium, Acanthocylium, Gastrochisma 

 (Lepidothynnus). Numerous fossil representatives in Tertiary 

 beds, belonging to Scomber, Auxis, Thunnus, Cybium, and to the 

 extinct genera Eothynnus, Isurichthys, Palimphyes, Scombrinus, 

 Sphyraenodus, Scombramphodon. 



These fishes, elegant in form and often in colour, are among 

 the swiftest of the inhabitants of the sea. Some are migratory, 

 like the Mackerel (Scomber scombrus) of the North Atlantic, 

 whilst others are remarkable for their wide distribution. The 

 Tunny (Thunnus thynnus\ for instance, the largest member of 

 the family, reaching a length of 10 feet, inhabits the Atlantic, 

 Pacific, and Indian Oceans, extending as far north as the British 



