422 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



along the straight portion of the lateral line. It is 

 vertically and usually horizontally expanded with 

 respect to other body scales, usually is thicker 

 and harder than other body scales, and the pos- 

 terior margin either terminates in a posteriorly 

 projecting, flattened or slightly elevated spine, 

 or ends in an apex, with the angle of the scute 

 formed by this margin being not greater than 110° 

 to 120°. In the following accounts, a reference to 

 scutes having completed their development im- 

 plies that they have developed the structural 

 characters that will fit this definition. The physi- 

 cal development of enlarging and hardening con- 

 tinues with growth of the fish. 



Scales in the straight lateral line which have not 

 developed the structural characters defined here, 

 but whose positional relationship indicates that 

 they would have become completely developed 

 scutes, are termed "developing scutes." 



Counts. — Scutes were counted on both sides of 

 the fish from the most-anterior to the most- 

 posterior completely developed scute. 



Relationship. — The mean of the number of 

 scutes of the right and left sides was used because 

 approximately 80 percent of the specimens ex- 

 amined showed an individual bilateral variation 

 in this character. This variation on individual 

 specimens examined ranged from 1 to 5 scutes in 

 hippos, 1 to 4 in latus, crysos, and ruber, and 1 to 3 

 in bartholomaei. There was little correlation of 

 this feature with the length of the fish, except that 

 more variation was found at the smallest sizes 

 (less than 30 mm. standard length) when the first 

 scutes to complete their formation do so rapidly. 

 Explanation. — Some scutes immediately fol- 

 lowing the most-anterior completely developed 

 scutes may not end in a spine or an apex — on 

 smaller fish they have not completed development 

 and on larger fish they may represent scutes winch 

 will never develop spines or whose weak spines 

 have worn off; in either case they are included in 

 the scute count. 



Nichols (1920b: 29) remarked, "The most an- 

 terior scutes near the angle of the lateral line are 

 small and poorly developed and the most posterior 

 ones minute, so that the personal equation enters 

 into their count somewhat." This applies more 

 to the smaller forms, for in most specimens of 

 more than 100 mm. the scutes are completely 

 developed to the point of junction with the curved 

 part of the lateral line and the terminal scute at the 



caudal base has a strong spine. Because of the 

 variation in scutes in smaller fish, and because the 

 adult complement of scutes is not present until the 

 fish has grown to a size greater than 100 mm., I 

 have applied an exacting definition and count. 

 This has resulted in my counts being lower for 

 fish of less than 100 mm. than are those usually 

 given in the literature; but the counts on larger 

 fish should approximate previous counts within the 

 limits of personal bias. Use of the mean number 

 of scutes will result in ranges being less variable 

 than is the case when scutes are counted on only 

 one side of a fish. 



Ontogeny. — The first scutes to complete their 

 development are located near the posterior two- 

 thirds of the straight part of the lateral line, and 

 the extent of development of the other scutes is 

 graduated from these toward both ends of the 

 lateral line. 



LATERAL LINE 



Measurements. — The curved part of the lateral 

 line was measured as a chord of the arch from its 

 junction with the upper edge of the shoulder girdle 

 to its junction with the straight part of the lateral 

 line. The straight part of the lateral line was 

 measured from its junction with the curved part 

 of the lateral line to its termination on the caudal 

 fin; on fish less than about 16 to 18 mm. standard 

 length, the formation had not progressed poste- 

 riorly to the caudal base, but the measurement 

 was taken to the caudal base. Measurements 

 were taken on both sides of the fish. 



The point of junction of the two parts of the 

 lateral line on some fish was marked by an abrupt 

 upturning of the curved part, and on others by a 

 gradual upturning — which forced an estimation of 

 this point. By definition, this point occurs where 

 the curved part bends upward from the straight 

 part. The straight part that continues forward 

 with no scutes or pores marking the continuation 

 is called the false lateral line and is difficult to see 

 on most Caranx. 



The extension of the lateral line onto the caudal 

 fin in the species of Caranx examined is contrary 

 to a statement by Gill (1883: 488) in his descrip- 

 tion of characteristics of the family: "Lateral line 

 continuous to and ending at the base of the 

 caudal fin." 



Ratio.— The mean of the quotients, obtained 

 by dividing the length of the straight part of the 



