Artificial Key to Families of Common Fishes 



1 . Mouth, suckerlike disc without jaws; no paired fins 



PETROMYZONIDAE (p. 67) 



Mouth with jaws; one or two pairs of paired fins 2 



2. Tail heterocercal (Diagram 3) 3 



Tail homocercal (Diagram 3) 6 



3. Tail typically heterocercal with well-defined ventral lobe; mouth sub- 

 terminal 4 



. Tail heterocercal but with rounded ventral lobe obliterated; mouth termi- 

 nal 5 



4. Long, paddlelike snout nearly one-half length of body; body naked; minute 



barbels present polyodontidae (p. 73) 



Short, flat snout; body with bony plates; well-developed barbels present in 

 front of mouth acipense2{idae ({>. 7.5) 



5. Rhombic ganoid scales; short dorsal fin, base less than height; long jaws 



LEPISOSTEIDAE (p. 81) 



Cycloid scales; long dorsal fin, base many times height; jaws moderate .... 



AMIIDAE (p. 85) 



6. Ventral, or pelvic, fins absent; body eellike anguillidae (p. 192) 



Ventral, or p)elvic, fins present; body not eellike 7 



7. Ventral fins abdominal (see page 58) 8 



Ventral fins jugular or thoracic (see page 58) 20 



8. Dorsal fin preceded by free dorsal spines (Figure 55) 



GASTEROSTEIDAE (p. 255) 



Dorsal fin not preceded by free dorsal spines 9 



9. Dorsal fin divided into two parts, or with separate adipose fins behind 



(Diagram 1; Figure 9) 10 



Dorsal fin single; no adipose fin present 14 



10. Anterior part of dorsal fin very small, of 3-8 slender, flexible spines; the 

 posterior part much larger and consisting of soft rays 



ATHERINIDAE (p. 245) 



Anterior dorsal fin large; jxjsterior adipose fin present, fused with caudal fin 

 in a few species 11 



11. No scales; barbels on head; single stout spine in dorsal and p)ectoral fins. . . . 



AMEIURIDAE (p. 169) 



Scales present; barbels absent; pectoral fins without spines 12 



12. Scales ctenoid; anterior dorsal fin with 2 weak spines, .percopsidae (p. 197) 

 Scales cycloid; dorsal fin without spines 13 



13. Mouth weak; teeth vestigial or absent; scales large, less than 100 in lateral 



fine COREGONIDAE (p. 94) 



Mouth strong; teeth well developed; scales small, more than 100 in lateral 



line SALMONIDAE (]). 105) 



14. Head scaly or partially scaly 15 



Head without scales 17 



64 



