320 FISHES OF ILLINOIS 



Order ACANTHOPTERI 



the spiny-eayed fishes 



Skeleton bony; the anterior vertebrae unmodified and without Weberian 

 ossicles; ventral fins more or less anterior (thoracic) in nearly all forms, 

 being abdominal in a few of the more archaic famihes; ventrals typically with 

 1 spine and 5 soft rays; anterior rays of dorsal and anal typically simple (un- 

 segmented) and spinous; shoulder girdle attached to the skull by a post- 

 temporal; no mesocoracoid, so far as known; hypercoracoid usually perforate; 

 opercular apparatus complete; border of mouth formed by the premaxillaries 

 alone, which are usually dentigerous; maxillary always present and toothless, 

 normally distinct from the premaxillary; air-bladder typically without duct 

 in adult; scales usually, though not always, ctenoid. 



To this group belong the great majority of existing marine 

 fishes, as well as numerous famihes more or less peculiar to fresh 

 water. At least 5 more or less distinct suborders of Acanthop- 

 teri are represented in the waters of Illinois, by far the greater 

 number of the species belonging to the perch-like or bass-like 

 families of the group Percoidei. 



Key to Families of ACANTHOPTERI found in Illinois 



a. Ventral fins abdominal, i. e., inserted nearer first (soft) rays of anal than to 



the angle under throat formed by the union of the free gill-membranes 

 (which definition does not include some members of the families Gasteros- 

 teidce and Percopsidw found outside of Illinois). 



b. Dorsal fin with a single spine or preceded by 4 or more free spines. 

 Suborder Hemibranchii. 



c. No adipose fin; dorsal fin preceded by 4 or more free spines. .Gasterosteidae. 

 Suborder Salmopercas. 



cc. An adipose fin: dorsal, anal, and ventral fins each with a weak and rather 



indistinct spine Percopsidse. 



Suborder Percesoces. 



bb. Dorsal fin preceded by a finlet of 3 to 8 slender spines Atherinidse. 



aa. Ventral fins thoracic, i. e., inserted nearer to angle of gill-membranes than 

 to the first anal spine, except in the deep-bodied genera Centrachidce 

 (which have dorsal spines 6 to 13 and anal spines 3 to 9 and ventrals 

 nearer to throat than to first soft ray of anal). 

 Group Percoidei. 



d. Ventral rays usually I, 7 (I, 6 or 7), never I, 5; vent jugular. .Aphredoderidse. 

 dd. Ventral rays I, 3 to I, 5, typically I, 5. 



e. Chin without barbel. 



f. Body scaled. 



