224 L. Agassiz on the I chthyological Fauna of Western America, 
Hybognathus nuchalis, Agass. 
For specimens of the species which constitute the type of this 
genus, I am indebted to Dr. Watson of Quincy, Illinois. - I have 
also received some from Dr. Rauch of Burlington, Iowa, and 
others from Dr. Engelman of St. Louis, Missouri. The largest 
specimens are nearly four inches long. The dorsal and ventral 
outlines are arched equally. The length of the head is one-fifth 
of the entire length or a little less than the greatest height of the 
body. The eye is of moderate size, and slightly elliptical in 
form, its hinder margin is nearer the posterior angle of the oper- 
cle than the end of the snout. The opercle is higher than 
long, its lower border is convex, the posterior emarginate. € 
upper maxillary does not reach the vertical line of the anterior 
border of the eye. The dorsal begins at.the highest part of the 
back slightly in advance of the ventrals; its height is greater 
than its length, and is not emarginated behind ; its last ray as to 
length, is to the longest ray of the fin as 1 to 2... The anal fin is 
one-third smaller than the dorsal. The lateral line is straight, 
except over the pectorals, where it bends upwards, and ends above 
the opercle. There are four rows of scales between this line and 
the ventrals, and five above it. 
ck, dark olive color, with a darker stripe from the neck to 
the base of the dorsal, extending also along the back, between — 
the dorsal and the caudal. A greyish, diffuse, longitudinal band 
above the Jateral line; sides silvery. © : 
P. 1,14; D.2, 1,62; V.1,7; A. 2,1, 62; 0.4, 1 9,8, [ 6. 
In the method adopted by Valenciennes, all the fishes of the fam- 
ily of Cyprinoids described above from the North American cont- 
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