FAMILY IV. CATOSTOMID^E. 25 



b. Scales small, more than 55 in the lateral PAGE 



series; air bladder in two parts, 

 c. Scales very small, more than 80 in the lateral 

 series; jaws with hard sheathes; under lip 

 very broad and deeply incised; fontanelle 



wanting, or very small in the young Pantosteus 30 



cc. Scales moderate, less than 80 in the lateral 

 series; fontanelle present in the adult. 



d. Nuchal region without a hump Catostomus 31 



dd. Nuchal region developed in a high sharp- 

 edged hump Xyrauchen 33 



bb. Scales large, less than 45 in the lateral series; 



air bladder in 3 parts ; lateral line complete .... Myzostoma 3 4 



Subfamily Ichthyobinae. 

 9. Carpiocles Rafmesque. 



Carpiodes Rafinesque, Ichth. Ohiensis, 56, 1820. (Type, Catostomus 

 . cyprinus Le Sueur.) 



Head comparatively short and deep, its upper surface always 

 rounded; mouth small, horizontal and inferior; suborbital bones well 

 developed; fontanelle present; lips thin or moderately thick, more or 

 less plicate; pharyngeal bones very thin; teeth compressed, nearly 

 equally thin all along the length of the bone, forming a fine, comb- 

 like crest of minute serratures; gill rakers slender and stiff above, 

 becoming reduced downward ; caudal peduncle rather short and deep ; 

 scales large, about equal all over the body; lateral line well developed, 

 nearly straight; dorsal fin long, with 23 to 30 rays; caudal fin forked, 

 lobes about equal. The fishes of this group reach a large size. They 

 inhabit the larger streams of the Mississippi Valley, extending as far 

 south as the Rio Usumacinta in Guatemala. 



KEY TO SPECIES OF CARPIODES. 



a. Tips of pectoral fins reaching nearly or quite PAGE 



to base of ventrals; lips moderate, 

 b. Dorsal rays 28 or 30; scales 40 in the lateral 

 series; depth 2|; lower lip slightly thicker 



than the upper meridionalis 26 



bb. Dorsal rays 24; scales 36 in the lateral series; 



depth 2f tnmidus 26 



aa. Tips of pectoral not nearly reaching base of 

 ventral; distance from tip of pectoral to base 

 of ventral about half the length of pectoral fin. 



