CLASSIFICATION OF FISHES 27 



b. Sucking disk on breast. Rotund, scaleless 

 with rows of hard nodules. Cyclopteridce 



C. Not as above. 



a. A single back fin, entirely of soft rays or with 

 one initial spine, sometimes a second small 

 adipose fin, ventral fins present. 



(I) Shark-shaped. Upper lobe of tail fin the longer. 



Mouth on under side of head, snout rather long, 



pointed. No scales, but rows of rough plates of 



different sizes. Acipenseridce 



(II) Lower lobe of forked tail fin the longer. Pectoral fins 



very large, used as support in gliding flight through 



the air. Exoccetidoe 



(III) Tail fin not notably unsymmetrical. 



(1) A small adipose fin on the posterior part of the back. 



(A) Mouth surrounded with barbels, body scaleless. 



Back and breast fins with a stout initial spine. 



SiluridoB 



(B) No barbels, body covered with small scales. 



(a) Ventral fins about under the back fin. Mouth 

 moderately large. 



x. Scales very small scarcely evident. 



SalmonidoB 



y. Scales larger, about 68 in a length- 

 wise series. A small silvery- 

 sided fish. ArgentinidcB 

 (b) Ventral fins before the back fin. Mouth very 

 large. Color mottled. Marine. 



Synodontidce 

 (2) No adipose back fin. 



(A) Teeth in the mouth small or absent. 



(a) No teeth in the small or moderate sized mouth. 



Lower pharyngeal bones with one or more 



rows of teeth. Tail fin usually moderately 



forked. Strictly fresh-water species. 



x. A small, thick-lipped, sucking mouth, 



opening downward. Pharyngeal teeth 



in a single comb-like row. Catoxlomidce 



