212 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



outer margin. The peduncle of the symphysis is much longer propor- 

 tionally, and more pointed than in Carpiodes and Bubalichthys. The 

 teeth are very numerous, small, thin and compressed in Carpiodes, but 

 the lower ones are gradually larger than the upper ones. Their inner 

 edge is slanting outwards, and not uniformly arched as in Bubalichthyx, 

 or truncate as in Cycleptus, the innermost margin rising somewhat in the 

 shape of a projecting cusp. Gill-rakers of anterior arch long and slender 

 above, becoming shorter downwards. 



Body heavy, robust, not especially arched above nor greatly com- 

 pressed, the form somewhat elliptical, the depth 2J to 3 in the length 

 of the body. 



Scales large, thick, nearly equal over the body, their posterior edges 

 somewhat serrate, the lateral line well developed, but not as distinct as 

 in Carpiodes, slightly decurved anteriorly, the number of scales in its 

 course 36 to 42; 13 to 15 in a transverse series from dorsal to ventrals. 



Dorsal fin with an elongate basis, its number of rays 25 to 30, the 

 anterior rays somewhat elevated, their length about half that of the 

 base of the fin ; caudal not much forked ; anal fin not much elevated, 

 its rays about 9 in number; pectorals and ventrals moderate, HIP latter 

 with about 10 rays. 



Sexual peculiarities, 'if any, unknown. Coloration dark, not silvery, 

 above dusky olive ; lower fins more or less black. 



Air-bladder with two chambers. 



Siza very large. 



The claim of this group to generic rank has been questioned by Pro- 

 fessor Cope and others. The differences in the pharyngeal teeth are 

 perhaps hardly sufficient to distinguish it from Carpiodes, but at present 

 I am inclined to think that the great development of the mandible, 

 which forms a large and terminal mouth, amply sufficient for generic 

 distinction. The relations of the group to Bubalichthys are doubtless, 

 in reality, closer. Ichthyobus bears much the same relation to Buba- 

 lichthys that Chasmistes does to Catostomus* and, so far as the mouth is 

 concerned, but in a greater degree, that Erimyzon bears to Minytrema 

 and Placopharynx to Myxostoma. The head of Ichthyobus is much larger 

 and stouter, and the whole body more robust and less compressed than 

 \n Carpiodes. I know from autopsy but a single species of Ichthyobus. 

 It has, however, been described under several different names. So far 

 as is known, the genus is confined to the valley of the Mississippi, no 

 species having been recorded from the Great Lakes, or from any streams 



