220 FISHES OF ILLINOIS 



Order ACANTHOPTERI 



(the spiny-rayed fishes) 



Skeleton bony ; the anterior vertebras 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. 



To 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 A canthopteri 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) ra3^s 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 Percopsidcc found outside of Illinois). 



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

 Suborder Hemibranchii. 



c. Xo adipose fin; dorsal fin preceded by 4 or more free spines. . . .Gasterosteidas. 

 Suborder Salmopercae. 



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

 indistinct spine Percopsidae. 



Suborder Percesoces. 



bb. Dorsal fin preceded by a finlet of 3 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 Centrachida- (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. . Aphredoderidae. 

 dd. Ventral rays I, 3 to I, 5, typically 1,5. 



e. Chin without barbel. 



f . Bod V scaled. 



