PRELIMINARY OBSERVATIONS. 53 



the names of the fins, which are not only im- 

 portant organs, but afford, by their structure, 

 position, and number, definite characters for 

 the establishment of orders, families, and ge- 

 nera. They are supported by bony or by car- 

 tilaginous rays ; they are thus designated : 



* 



Dorsal fins, on the back, D D. Pectoral fins, p. 

 Ventral fins, v. Anal fin, A. Caudal fin, C. 

 The formula for expressing the number of fins, 

 the number of fin-rays and their condition, 

 taking the perch by way of example, is thus 

 written, D 15. 1 + 13. P 14. v 1 + 5. A 2 + 8. 

 C 17. The meaning is as follows : D, dorsal fin, 

 has fifteen rays, all spinous ; the second dorsal 

 fin has one ray spinous + 13 that are soft. 

 p, pectoral fin, with 14 rays soft, v, ventral fin 

 with one ray spinous + 5 soft. A, anal fin, 

 with 2 rays spinous + 8 soft, c, caudal fin, 

 with 17 rays. 



Along the sides of fishes is a row of scales, 



