248 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. VII. 



aa. Pharyngeal teeth fewer, 4 to 8 on each bone; dorsal fin of less 

 than 10 rays; lips without thickened skin. Cyprinidce, 257 



Family Catostomidse. 



THE SUCKERS. 



Body oblong or elongate, usually more or less compressed and 

 covered with large cycloid scales; fins without true spines; gill 

 membranes united to the isthmus ; pseudobranchias present ; branchi- 

 ostegals 3 ; margin of upper jaw formed in the middle by the small 

 premaxillaries and on sides by maxillaries; lower pharyngeal bones 

 falciform and with a single row of comb-like teeth ; mouth with thick 

 lips covered with plicate or papillose skin ; fins without spines ; caudal 

 fin forked; no pyloric cceca; air bladder in 2 or 3 parts, connected to 

 oesophagus. 



a. Dorsal fin elongate, of more than 20 developed rays. 



b. Mouth large, more or less terminal, protractile forward; 

 * pharyngeal teeth and bones moderate; coloration, dark. 



Ictiobus, 249 



bb. Mouth smaller, inferior, protractile downward; pharyngeal 

 bones narrow, with the teeth thin and weak; coloration, pale. 



Carpiodes, 250 

 aa. Dorsal fin shorter, of less than 20 rays. 



c. Lips plicate. 



d. Lateral line wanting or imperfectly developed ; sides with dark 

 band or dark lateral stripes ; air bladder in 2 parts. 



e. Lateral line entirely wanting; sides with a single dark lateral 

 band. Erimyzon, 251 



ee. Lateral line incomplete; sides with dark lateral stripes along 

 the rows of scales. Minytrema, 252 



dd. Lateral line complete; sides without dark lateral band or 

 lateral stripes ; air bladder in 3 parts. 



f . Pharyngeal teeth compressed ; mouth wholly inferior. 



Moxostoma, 253 



ff. Pharyngeal teeth large, molar-like; mouth somewhat oblique. 



"\(Placo pharynx) 



* The pharyngeal bones are situated on either side of the oesophagus just 

 back of the gill arches. 



t Placopharynx duquesnii (Le Sueur) probably does not occur in the waters 

 in and about Chicago. In form and appearance it resembles the common red- 

 horse, with which it is often identified, but from which it is easily separated 

 because of its molar-like pharyngeal teeth. 



