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; vertebra usually in moderate numbers; ventrals 



ordinarily present ; mesocoracoid present Isospondyli. 



hh. Body eel-shaped; vertebrae very numerous, 1*00 to 250; no ventral fins; 



mesocoracoid wanting Apodes. 



gg. Anterior (3 or 4) vertebra; 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 rudimentary 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 Salmopcrccs.) 

 kk. Duct to air-bladder wanting. 

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

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



esoces.) 

 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. 



