220 FISHES OF ILLINOIS 



Order ACANTHOPTERI 



(the spiny-rayed 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 families; ventrals typ- 

 ically with 1 spine and 5 soft rays; anterior rays of dorsal and anal 

 typically simple (unsegmented) and spinous; shoulder girdle attached to 

 the skull by a post-temporal; no mesocoracoid, so far as known; hyper- 

 coracoid usually perforate; opercular apparatus complete; border of 

 mouth formed by the premaxillaries alone, which are usually dentiger- 

 ous; maxillary always present and toothless, normally distinct from the 

 premaxillary ; air-bladder typically without duct in adult; scales usually, 

 though not always, ctenoid. 



T( i this group belong the great majority of existing marine fishes, 

 as well as numerous families more or less peculiar to fresh water. At 

 least 5 more or less distinct suborders of Acanthopteri are represented 

 in the waters of Illinois, by far the greater number of the species be- 

 longing 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 

 teidcB and Percopsida: found outside of Illinois). 



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

 Suborder Hemibranchii. 



c. No adipi ise tin . di irsal tin preceded by 4 or more free spines. . . . Gasterosteidae. 

 Suborder Salmopercae. 



cc. An adipose tin; dorsal, anal, and ventral tins each with a weak and rather 



indistinct spine Percopsida;. 



Suborder Percesoces. 



bb. Dorsal fin preceded by a finlet of .i to 8 slender spines Atherinidae. 



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 Centrachides (which 

 have dorsal spines 6 to 13 and anal spines .1 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. . Aphredoderidae. 

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



e. i 'iiin without barbel. 



f. Mi "I v sealed. 



