GEN. SCOMBER. THE COMMON MACKEREL. 187 



sidered separately, these fish are easily characterized. 

 The separation of the posterior rays of their second 

 dorsal fin, and of their anal, suffice for that purpose 

 in the Mackerel and Tunny, the typical genera of 

 the family. But these are only the chiefs of a 

 numerous series of genera and sub-genera, in 

 which the general characters alter by degrees, and 

 pass insensibly into others. The possession of scales, 

 so small as to make the greater part of the skin 

 appear as if it were smooth, the vertical fins free 

 from scales, and the gill-covers without spines or 

 denticulations, constitute almost all the prevailing 

 characters which can be assigned to the family; 

 and notwithstanding they have a resemblance which 

 never leaves them in any of their modifications, so 

 that they form what Botanists call a family by series 

 or transition. The caudal fin is often of great 

 size and power, and the sides of the tail are keel- 

 shaped, and armed with scales or shields. This 

 family is one of the most useful to man, many of 

 the species constituting excellent food, their size 

 being considerable, and their reproduction enormous, 

 bringing them periodically to the same latitudes, and 

 so making them the object of most extensive and 

 important fisheries. It is subdivided into four 

 great sections. THE FIRST having the anterior 

 dorsal fin entire, and the terminal rays of the pos- 

 terior detached or insulated, forming what may be 

 called spinous fins, pinnce spurice, or finlets. To 

 this subdivision belongs the 



Gen. XXII. SCOMBER. Mackerels. Characterized 



