How to Identify a Fish 



the alternative which is under the same letter doubled, and pro- 

 ceed as before. In a few instances there is a second or even 

 third alternative, the guide letter being written three or four times 

 to correspond, as, for example, "III" in the Key to Families. 



If you do not know to what family the specimen in hand 

 belongs use the Key to Families at the close of the volume where 

 all the family names are numbered and paged to correspond with 

 their position in the text. When the family is found and its 

 important characters studied, the key following the family diagnosis 

 will lead one to the right genus. If the specimen agrees with the 

 generic diagnosis given, you can be sure that no mistake has been 

 made thus far and the particular species can be determined by the 

 use of the key following. 



These keys and descriptions may at first seem somewhat 

 difficult but with a little experience they become exceedingly 

 easy to use and understand. 



In descriptions of fishes certain comparative measurements are 

 made. The length of the head and the depth of the body are 

 always compared with the standard length of the fish, which is 

 the distance from the tip of the snout to the base of the caudal 

 fin. The diameter of the eye, length of snout, maxillary, and 

 mandible, and (usually) the length of fins, spines or rays, are 

 compared with that of the head. 



In our descriptions of species, we have attempted to bring the 

 principal comparative measurements first. The expressions "head 

 4 ", or "depth 4", mean that the length of the head in the one 

 case, or the greatest depth of the body in the other, is contained 

 4 times in the length of the fish measured from the tip of the snout 

 to the end of the last caudal vertebra, the caudal fin being not 

 included. "Eye 5" means that the horizontal diameter of the eye 

 is contained 5 times in the length of the head. "Scales 1 1-85-25" 

 means that there are 1 1 rows of scales between the front of the 

 dorsal fin and the lateral line, 85 scales in the lateral line itself, 

 and 25 scales in an oblique series downward and backward from 

 the lateral line to the origin of the anal fin, or the vent. When 

 the number of pores in the lateral line is fewer than the number 

 of scales, we have usually indicated the fact. The fin formulas 

 are usually shortened as much as possible; thus " D. 10"; "D. 

 V, 9"; or " D. VIII-I3", means that in the first case the fish 

 has a single dorsal fin of 10 soft or articulated rays; in the second 



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