Perca jiavescens D. XIII, 14 means that the dorsal fin of the yellow perch 

 usually has thirteen spines and fourteen rays. The spiny portion of the dorsal 

 fin is usually partly, sometimes wholly, separated from the rayed portion. Since 

 the rays are branched, care must be taken to count the bases. In the spinyfinned 

 fishes there are usually spines in the anal, and often in the pectoral, fins. The 

 Ameiuridae, Salmonidae and a few other families have an additional dorsal fin, 

 posterior to the rayed one and unsupported, in native species, by any rays or 

 spines. This is called the adipose fin. Sometimes its posterior margin is adnate 

 or joined to the fish's back, in which case the student may overlook it or mistake 

 it for part of the tail fin. Of the paired fins, the position of the pelvics is most 

 helpful in identification. Regardless of their position antericposteriorly, they 

 are always more ventral than the pectoral fins, and arc sometimes called the 

 ventral fins. It is well to remember this, for m some families, including the 

 cods (Gadidae) , they are actually anterior to the pectoral fins. This position 

 is described as jugular. If they lie almost directly below the pectorals, as in the 

 darters (Etheostoviidae) they are said to he thoracic. In the minnow and 

 sucker families (Cyprmidae and Catostomidae) they are quite posterior and 

 are said to be abdominal in position. In the sticklebacks (Gasterosteidae) , the 

 pelvic fins are usually almost central, but are called subabdominal. 



Lateral Line 



The lateral line is the external indication of a complicated sense-organ 

 system of canals covering the head and extending along the sides of the body. 

 Small openings from each canal are usually shown by small openings or tubes 

 in some of the scales. The line so formed may be evident along the whole side 

 and even on the tail, or it may be only partially evident. On some fishes it 

 forms a relatively straight line, while on others it may curve up or dov/n, 

 possibly to avoid water currents produced by the pectoral fins Care must be 

 taken to avoid confusing the lateral line with a pigmented lateral stripe often 

 present. 



Scales 



The ganoid type of fish scale, a very hard, shining, rhombic one, is now 

 developed among North American fishes only by the gars as a complete cov 

 ering and by the sturgeons as a small patch on the upper lobe of the tail. Two 

 types of scales are found on the higher fishes. One type, the cycloid, is fairly 

 regularly oval. The other type, the ctenoid, has its free edge toothed. It 

 has been suggested that the type of scale might serve as a basis for classifica- 

 tion but, unfortunately for the idea, intermediate forms are found and in one 

 family one may find both types of scales. 



The number of scales is often useful as a diagnostic character, and a 

 system of recording has been developed. For example, 8'45'10 means that the 

 fish has 45 scales in the lateral line row or in a line from head to tail, eight 



250 



