L. Agassiz on the Ichthyological Fauna of Western America. 223 
Quincy, Illinois, to Dr. I. H. Rauch, for others from Burlington, 
Iowa, to Prof. J. M. Safford, for specimens from Lebanon, Ten- 
nessee, to Col. B. L. C. Wailes for others from Natchez, Mississippi; 
Ihave myself caught specimens at Beardstown and Lasalle, Illi- 
nois, I received from an unknown contributor, with many other 
species, one specimen from Rome, New York. I find it also 
among Professor Baird’s specimens from Westport (Lake Cham- 
plain) and among mine from Lake Huron. This most extraor- 
dinary range is hardly covered by a single species, and yet I can 
find no specific differences between the specimens even from the 
most remote localities. I must remark however, that from some 
I have only a few rather indifferently preserved specimens. 
Hybognathus, Agass. 
In this genus the body is more of a fusiform shape than in 
Pimephales; the head is triangular or wedge-shaped, and the 
snout hardly blunt ; the profile not descending suddenly on reach- 
ing the nostrils. The top of the head is convex and rounded at the 
sides instead of forming a prominent ridge. The mouth is small 
and terminal ; the lower jaw is quite thin and flat ; its symphy- 
Sis is angular and prominent, being surmounted by a slight tuber- 
_ ¢le, in allusion to which I have called the genus Hybognathus. ~ 
The upper jaw partakes in a less degree of the angular outline 
of the lower jaw, which is shorter than the upper, and fits within 
it. The dorsal and anal fius, though similar in form, yet differ 
from those of Pimephales, in having the longest simple ray the 
longest ray of the fin, making the anterior and outer angle 
pointed. The pectorals and ventrals are slender and pointed ; 
the caudal is deeply forked. The scales are as large on the back and 
Anterior portions of the body as behind the dorsal and ventral fins. 
Scales subtriangular, owing to the greater vertical diameter, the 
Prominent posterior margin and the very forward position of the 
centre of radiation. 
Ornamental concentric ridges closer together upon the very 
Narrow anterior field. No radiating furrows upon this, and the 
= Na ¢ and d, 
a the side, still more magnified. 
