228 FISHES. 



in the Mississippi Valley, every where forming a charac- 

 teristic feature of our fish-fauna. The genera are quite 

 well known, and most of them are firmly established; 

 but the species of some groups, particularly Ichthelis 

 and C ' hcenobryttus are in a state of almost inextricable 

 confusion. 



* Dorsal fin long, deeply divided, sometimes almost into two fins ; 

 dorsal spines 10, anal 3 ; opercle emarginate behind ; caudal 

 emarginate; an additional maxillary bone; mouth wide; 

 body moderately elevated. (MICROPTERIN/E.) 



MICROPTERUS, 1. 



** Dorsal fin continuous, without deep division, about equal to the 

 anal in extent; opercle emarginate behind, ending in two flat 

 points; a slender supernumerary bone attached along the 

 posterior margin of the broad flattish maxillary; soft fins 

 high, mottled. (CENTRARCHIN/E.) 



a. Spinous dorsal longer than soft part, forming an angle with 

 it; dorsal spines 11 or 12, anal spines about 8. 



CENTRARCHUS, 2. 



aa. Spinous dorsal shorter than soft part, continuous with it ; 



dorsal spines 6 to 8 ; anal spines normally 6. POMOXYS, 3. 



*** Dorsal fin without division, notably larger than anal. (IcH- 



THELIN.E.) 



f Anal with 5 or 6 spines ; dorsal with 10 to 12 ; opercle emar- 

 ginate behind ; a supernumerary maxillary bone. 



Scales ctenoid ; caudal emarginate ; fins mottled ; anal 



spines normally 6. . . AMBLOPLITES, 4. 



Scales cycloid ; caudal rounded ; fins plain ; anal spines 



normally 5. ... ACANTHARCHUS, 5. 



ft Anal with 4 spines ; dorsal with 8 ; caudal rounded. 



HEMIOPLITES, 6. 



fff Anal with three spines. 



b. Dorsal spines 9 (sometimes abnormally 8 or 10) ; caudal 

 rounded; opercle emarginate behind not ending in 



rounded flap ENNEACANTHUS, 7. 



bb. Dorsal spines 10 (rarely 9 or 11 in abnormal specimens.) 



