The Food of Fresh-Water Irishes. 445 



Pharyngeal jaws strong, thick, nearly twice as wide as high ; 

 teeth about thirty-five in number, the lower four or five much 

 thickened, occupying about one fourth the length of the jaw. 

 The crown is expanded transversely to the axis of the jaw, 

 rounded, not crenate or hooked. The crowns of the teeth above 

 the sixth or seventh are hooked and slightly crenate, but less so 

 than in Moxostoraa. Compared with that genus, both teeth and 

 jaws constitute a more effective crushing and grinding appara- 

 tus. 



The system of gill-rakers is similar to that of Moxostoma, 

 but is less effective as a strainer, the anterior row of the first gill 

 being less numerous, shorter, and thicker. These divide into two 

 sets of about equal length, the upper series projecting forward, 

 rather short, triangular, about one third the length of the cor- 

 responding filaments, fifteen or sixteen in number, the lower 

 series, five or six, in the form of low lamellar ridges. Rakers 

 of the other gills thick, lamellar, with tubercles on the free 

 edges ; corresponding lamella" on anterior margin of the 

 pharyngeal jaw. 



Alimentary canal about two and a half times the length of 

 the head and body. The alimentary structures in general in- 

 dicate better adaptation to molluscan food than those of the 

 stone roller, and inferior adaptation to Entomostraca. 



The number of specimens examined was too small to make 

 it worth while to report their food, especially as they were 

 evidently under size. The branchial and pharyngeal structures 

 and known habits of the species indicate that its food is not 

 especially different from that of Moxostoma, just discussed, 

 and it will probably be found to consist chiefly of Mollusca 

 and insect larva?, the former in larger ratio than in Moxostoma, 

 and in smaller ratio than in the species next to follow. 



Hypentelium nigricans, LeS. Stone Roller ; Hammer- 

 head. 



This curious fish, distinguished both in form and habit 

 from its allies of the family, occurs usually in rapid shallows 

 of clear streams, commonest to the northward. It is taken 

 rarely in lakes. 



