GENUS ICHTHYOBUS. '211 



slightly corrugated. The height of the body is contaiued thrice aud 

 one third or thrice aud one fourth in the total length (without caiuhil), 

 the length of the head four times or four times and a half ; head not 

 much longer than high. Eye rather small, one fifth of the length of the 

 head aud two thirds of that of the snout; suborbitals narrow. The 

 anterior dorsal rays are not much produced, being shorter than the 

 head. Caudal fin forked. The origin of the ventral fin is vertically 

 below the fourth dorsal ray. Pectoral fin not extending to the ventral. 

 There are five longitudinal series of scales between the lateral line and 

 the root of the ventral. Coloration uniform. Pharyngeal teeth very 

 numerous and small, increasing somewhat in size downwards. 

 "Eio Usumacinta (Guatemala)." 



Genus ICHTHYOBUS Rafinesque. 



Amblodon Rafinesque, Journal de Physique, de Cliymie et d'Histoire Naturelle, Paris, 



421, 1819. (Part.) 

 Icliobns Rafinesque, Ich. Oh. 1820, p. 55. (As subgenus of Catostomus.) 

 Ichthyobus Agassiz, Am. Jouru. Sci. Arts, 1855, p. 195. 



Type, Amhlodon bubalus Rafinesque. 



Etymology, IxO^'C, fish ; f^ovg, bull or buffalo ; i. e., buffalo-fish. 



Head very large and strong, wide and deep, its length 3.J to 3f in that 

 of the body, its upper surface broad and depressed ; eye moderate, 

 wholly anterior in position, the middle of the head being entirely behind 

 it ; .suborbital bones proportionately narrow; fontanelle large, well open: 

 opercular apparatus largely developetl, the subopercuium broad, the 

 operculum broad, strongly furrowed. 



Mouth very large for a Sucker, terminal, protractile forwards, the 

 middle of the premaxillaries rather above the line of the middle of the 

 eye, the posterior edge of the maxillary extending about to the line of 

 the nostrils; mandible very strong, oblique, placed at an angle of 45 

 degrees or more when the mouth is closed, its posterior end exteudiug 

 to beyond opposite the front of the eye, its length a little less than one- 

 third that of the head. Lips very little developed, the upper narrow 

 and smooth, scarcely appreciable, the lower narrow, rather full on the 

 sides, but reduced to a narrow rim in front, entirely destitute both of 

 papillae and i)lic8e; jaws without cartilaginous sheath; muciferous sys- 

 tem of head well developed ; isthmus narrow ; pharyngeal bones in form 

 intermediate between those of Carpiodes and those of BubaUchihys^ the 

 outer surface of the arch standing outwards, and presenting a porous 



