ICTIOBUS 73 



Distributed throughout the Mississippi Valley much as the 

 other buffalo are, but tending more generally to deep water, 

 according to the reports of fishermen. 



It is common in the Mississippi and the Illinois rivers, and 

 in the principal streams of the state at large. It is not so 

 frequently taken in shallow water as the other species, and it is 

 said to have a stronger preference for flowing streams. Never- 

 theless, it must be said that more than two thirds of -the speci- 

 mens in our collections came from lakes and sloughs, the greater 

 part of the remainder being from rivers of the larger size. 



This buffalo does not average as large as the preceding 

 species, its maximum weight in the Mississippi being, according 

 to Mr. Ashlock, of Alton, less than 40 Ib. 



About a fifth of the food of the specimens examined, con- 

 sisted of vegetation, mainly duckweed, but with an occasional 

 admixture of terrestrial rubbish. The animal food was divided, 

 with approximate equality, between mollusks, insects, and 

 Entomostraca, the latter taken chiefly in spring when they are 

 present in the greatest abundance. The food of the young of 

 this buffalo consists largely of the minuter forms of the plankton, 

 including especially Protozoa, rotifers, and unicellular algae. 



The gill-rakers of this species are less numerous than those of 

 cyprinella and scarcely so long, and seem to form a less efficient 

 straining apparatus. The pharyngeal jaws are heavier, triangu- 

 lar in section, and about as thick as high. Seventeen specimens 

 of this species, collected from the Illinois and the Mississippi in 

 various months from April to October, contained aquatic vege- 

 tation amounting to about a third of the total food, the principal 

 element being a small duckweed (Wolffia) especially abundant 

 where a part of the fishes were taken, and amounting in some 

 cases to 95 per cent, of the contents of the stomach. A larger 

 duckweed, fragments of horn wort (Ceratophyllum), diatoms, and 

 other unicellular algae had also been eaten. Animal food (80 

 per cent.) was fairly equally divided between mollusks, insects, 

 and Crustacea, the first (30 per cent.) being mainly a thin-shelled 

 bivalve (Sphcerium') common in the mud. Several specimens 

 had eaten nothing but this mollusk. Chironomus larvae and 

 Entomostraca were the principal other elements, each making 

 practically a fifth of the entire food. 



14 F 



