GENUS ERIMYZON. 141 



and oblique in position when, the mouth is closed, the mouth thus similar 

 to that of IchthyoTjus. Eye moderate, rather high up, placed about mid- 

 way of the head : suborbital bones considerably developed, not very 

 much narrower than the fleshy portion of the cheek below them, the 

 posterior suborbital concavo-convex, about twice as long as deep, some- 

 times divided, the anterior somewhat deeper than long, sometimes 

 divided into two, sometimes united with the preorbital bone, which is 

 well developed and much longer than broad. Opereular bones moder- 

 ately developed, scarcely or not rugose. Fontanelle evident, rather 

 large. Gill-rakers rather long, about half the diameter of the eye in 

 length. Isthmus moderately developed, about the width of the eye. 



Pharyngeal bones weak, the teeth quite small, slender, and weak, 

 rapidly diminishing in length upwards, each tooth narrowly compressed, 

 with a cusp on the inner margin of the cutting surface, and some ine- 

 qualities besides. 



Body oblong, rather shortened, heavy forwards and considerably com- 

 pressed. 



Scales rather large, more or less crowded forwards, sometimes showing 

 irregularities of arrangement, the longitudinal radiating furrows much 

 stronger than usual, the scales rather longer than deep, but so imbri- 

 cated in the adult that the exposed surfaces appear deeper than long. 



Lateral line entirely wanting. Scales in the longitudinal series from 

 head to base of caudal 35 to 45 in number ; scales in transverse row from 

 base of ventral to dorsal 12 to 18. 



Dorsal fin rather short and high, with from 10 to 14 developed rays, 

 the number usually 11 or 12. 



Beginning of dorsal fin rather nearer snout than base of caudal. Pec- 

 toral fins moderate, not reaching ventrals 5 the latter not to vent. 



Yentrals under a point rather in advance of the middle of dorsal ; 

 their rays normally 9, but occasionally 8 or 10. 



Anal fin high and short, more or less emarginate or bilobed in adult 

 males ; caudal fin moderately forked or merely lunate, its two lobes 

 about equal. 



Air-bladder with two chambers. 



This genus has a very wide range, one of its two known species 

 probably occurring in all the streams of the United States east of the 

 Eocky Mountains. 



The existence of this genus seems to have been first noticed by DeKay, 

 who, however, erroneously supposed it to be identical with the AM- 



