14 FISHES OF ILLINOIS 



f. Mesocoracoid present except in eel-shaped forms; air-bladder with open duct 



when present. 



g. Anterior vertebrae not modified, similar to the others, or more elongate, 



separate and not provided with Weberian ossicles. 



h. Body not eel-shaped; vertebras usually in moderate numbers; ventrals 

 ordinarily present; mesocoracoid present Isospondyli. 



hh. Body eel-shaped; vertebras very numerous, 100 to 250; no ventral fins; 

 mesocoracoid wanting Apodes. 



gg. Anterior (3 or 4) vertebrae modified, coossified and provided with a chain of 

 small bones (Weberian ossicles), connecting the air-bladder with the 

 auditory apparatus in typical forms; mesocoracoid present. 



i. Parietals distinct from the supraoccipital ; symplectic present ; maxillary per- 

 fect or (rarely) wanting Plectospondyli. 



ii, Parietals usually fused with the supraoccipital; symplectic absent, maxil- 

 lary imperfect, forming the base of a conspicuous barbel . . . Nematognathi. 

 ff. Mesocoracoid absent; body not eel-shaped. 



j. Air-bladder with open duct; no spines in fins; shoulder girdle connected with 

 the skull by a bifid post-temporal Haplomi. 



jj. Air-bladder with a rudimentary duct or with duct obsolete; dorsal fin with 

 one or two rudiinentary spines, with two or more free spines, or preceded 

 by a finlet of four or more spines .... Acanthopteri (with abdominal ven- 

 trals). 



k. Air-bladder with rudimentary duct. (Suborder Salmopcrcce.) 



kk. Duct to air-bladder wanting. 



1. Dorsal fin preceded by two or more free spines. (Suborder Hemihranchii.) 



11. Dorsal fin preceded by a finlet of four or more spines. (Suborder Perc- 

 csoces.) 



ee. Ventral fins thoracic or jugular, spines typically, though not always, present 

 in the fins. 



m. Pelvic girdle more or less solidly attached to the clavicular arch; spines 



ordinarily present in the fins Acanthopteri (with thoracic ventrals). 



Including the great group of scombriform and perciform fishes and their 

 allies. 



mm. Pelvic bones loosely attached to the clavicular arch by ligament: fins with- 

 out spines; tail isocercal, the hippural not expanded Anacanthini. 



