MACKERELS. 457 



Scomhridce are well represented in tertiary formations : in 

 the Eocene schists of Glaris two extinct genera, Palimphyes 

 and Isurus, have been discovered. In Eocene and Miocene 

 formations Scomber, Thynnus, and Cylium are not uncommon. 



Scomber. — The first dorsal continuous, with feeble spines ; 

 five or six finlets behind the dorsal and anal. Scales very small, 

 and equally covering the whole body. Teeth small. Two short 

 ridges on each side of the caudal fin. 



Mackerels proper are found in almost all temperate and 

 tropical seas, with the exception of the Atlantic shores of tem- 

 perate South America, where they have not been found hitherto. 

 In Europe, and probably also on the coast of England, three 

 species occur : S. scomber, the common Mackerel, which lacks 

 an air-bladder ; ^S*. pneumatopliorus, a more southern species, 

 with an air-bladder ; and S. colias, like the former, but with 

 a somewhat different coloration, and often called " Spanish " 

 Mackerel. On the Cape of Good Hope, in Japan, on the 

 coast of California, in South Australia, and New Zealand, 

 Mackerels are abundant, which are either identical with, or 

 very closely allied to, the European species. On the coasts 

 of the United States the same species occur which tenant the 

 western parts of the Atlantic. Altogether seven species are 

 known. 



Thtnnds. — The first dorsal continuous, with the spines rather 



Fig. 205. — Thynnus thynnus. 

 feeble ; from six to nine finlets behind the dorsal and anal. 



