34 VERTEBRATE ANIMALS OF THE UNITED STATES 



di Ventral fins present. 



Ci Branchiostegal rays 6 or more i. Isospondyli. 



e2 Branchiostegal rays 3. 



fi Pseudobranchiae present (rarely absent) 3. Eveniognatkl. 



ii Pseudobranchiae absent (but one species in 



United States) 4. Heterognathi. 



ds Ventral fins absent; eels 2. Apodes. 



Co Body without scales; dorsal and pectoral fins each with 



a strong spine; catfish 5. Nomitognalhi. 



bo Head more or less scaly. 



Ci Lateral line absent or, when present, median in position. 6. Haplonii. 

 Co Lateral line extends along the side of the abdomen 



(but one species in United States) 7. Synciitogiiathi. 



&2 Ventral fins mostly thoracic or jugular (Fig. 3), typically with 

 I spinous and 5 soft rays each ; anterior rays of dorsal, anal 

 and pectoral fins usually spinous 8. Acanthoptcri. 



Order i. Isospondyli. — Herring; salmon; trout. Fishes with 

 unmodified anterior vertebrae; lower pharyngeal arch simple, not 

 falciform; head not scaly; maxillary distinct from the premaxillaries 

 and forming part of the margin of the upper jaw; no barbels; air bladder, 

 if present, with a pneumatic duct; fins without spines; ventral fins 

 abdominal; scales usually cycloid, sometimes ctenoid, occasionally 

 wanting: 20 to 25 families, mostly marine; 6 families in fresh water. 



Key to the Fresh Water Families of Isospondyli 



ai No adipose fin present. 



bi Lateral line present i. Hiodontidcc. 



bo Lateral line absent. 



Ci Last rays of dorsal fin much elongated 2. Dorosomidce. 



Co Dorsal fin normal 3. Cliipeidcc. 



a2 Adipose fin present. 



bi Branchiostegals 10 to 20 4. Salmonidcc. 



hi Branchiostegals 6 to 10. 



Ci Dorsal fin very long 5. Thymallidce. 



C2 Dorsal fin short 6. Argnitinidce. 



Family i. Hiodontidae. — The mooneyes. Body oblong, com- 

 pressed, covered with silvery cycloid scales, short; mouth terminal, 

 oblique; tail forked; branchiostegals 8 to 10; lateral line present; 

 teeth on jaws, margin of the tongue, vomer, sphenoid, hyoid, pterygoid 

 and palatines; eyes very large; no pseudobranchiae; i pyloric appendage: 

 I genus. 



Hiodon LeSueur. With the characteristics of the family: 3 species, 

 all of little food value. 



