the Ichthyoloyy of Australia. 25 



and the first very short dorsal spine stands upon it. The whole of 

 the branching dorsal and anal rays are connected by a membrane, 

 which is notched before the more posterior rays. The lateral line is 

 slightly arched before the dorsal fin. It makes a small obtuse angle 

 over the middle of the pectoral, not more conspicuous than three or 

 four undulations, which follow at a little distance : after passing the 

 first four jointed rays of the dorsal, the line runs perfectly evenly and 

 directly to the caudal fin. 



Rayb:— D. 7|— 1|19; A. 2— 1\17 ; C. 18|; P. 17; V. 1|5. 



Dimensions, inches, line.. 



Length from tip of snout to end of caudal fin 19 8 



base of ditto 16 4 



beginning of jointed dorsal 8 9 



anus 6 3 



first free dorsal spine 5 4 



edge of gill- cover 3 6 



edge of orbit 8 



Diameter of the eye 8 



Length of pectorals 2 2 



Height of dorsal and anal 2 6 



Depth of caudal fork 2 9 



Height of body, about 5 



The Caranx trachurus, Scad or Horse-mackerel, is an almost 

 cosmopolitan fish ; or at least, the peculiar characters of the 

 species which inhabit the various districts of the ocean, if they 

 be different, are not very obvious. There are variations of 

 form in the Trachuri of the European seas, which appear, when 

 a great number of individuals are examined, to pass into each 

 other by such insensible gradations, that Cuvier hesitates to 

 consider them as permanent, and merely divides the species 

 into three groups of varieties. In the first group, which fur- 

 nishes the example chosen for description in the ' Histoire des 

 Poissons/ the lateral line is armed with seventy shields, and 

 its oblique bend extends from opposite the beginning of the 

 second dorsal to beneath the tenth ray. The second group 

 comprises individuals having from eighty to eighty-eight 

 shields, of less vertical height, and rather more than half of 

 the lateral line posterior to the bend, which is also more sud- 

 den. The third group, which includes individuals possessing 

 from ninety-four to ninety-nine lateral shields, is, in Cuvier^s 

 opinion, actually a distinct species, though he does not give 

 it a name. Its members have a more slender body than the 

 ordinary species, a narrower lateral line, which bends sud- 

 denly in the middle, and leaves the posterior part just equal 

 to the anterior part, including the bend. 



Scad differing very slightly from the European ones, and 

 having from seventy-three to seventy-five lateral shields, are 

 noticed in the ' Histoire des Poissons' (ix. p. 19) as having 



