L. Agassiz on the Ichthyological Fauna of Western America. 85 
though they bear only a remote resemblance to it. I have been 
unable to trace the etymology of the name Moxostoma. It may 
be a misspelling for Myzostoma, but in that form the name is 
already applied to a genus of worms. 
The species of this genus contrast greatly with those of all 
other genera of the family of Cyprinoids, by the total absence of 
external openings in the lateral line, visible upon the scales. There 
is indeed no row of perforated scales upon the sides of the body to 
mark the main course of the system of tubes, pervading the skin 
in most fishes, and the pores traversing the skin which covers the 
skull and cheeks, as well as the lower jaw, are so minute as to 
line is distinctly marked by a series of tubes traversing a promin- 
ent row of scales along the sides, and extending through the mas- 
toids to the forehead, and along the preopercle to the symphysis 
of the lower jaw. This total absence of an externally visible lat- 
eral line is compensated by the presence of a few deeper radia- 
ting furrows in the posterior field of all the scales.* 
The longitudinal diameter of the scales exceed greatly the 
transverse, but the scales are imbricated in such a manner that 
the portion visible externally appears higher than long. The 
centre of radiation is placed in the middle of the scales; there 
are no radiating furrows upon the lateral fields, those of the pos- 
terior field are fewer and deeper than those of the anterior field ; 
the concentric ornamental ridges of the posterior field are also 
much broader and farther apart than those of the lateral and an- 
terior fields. The scales are smaller upon the anterior portion of 
the body than upon the sides. Another remarkable peculiarity 
of this genus consists in the great difference there is among the 
aduits in the form of their fins in the different sexes. The young 
also differ strikingly from the adults both in form and coloration : 
the mouth is not surrounded by such thick lips, nor turned so 
far downwards, so that they may easily be mistaken for young 
Leucisci, and as they are marked with a broad, longitudinal black 
band extending from the snout through the eye to the end of the 
tail, they bear the closest resemblance to the Cyprinus atronasus 
of Mitchill, (my Rhinichthys atronasns) and have more than 
Once been mistaken for that species. This lateral band which I 
have observed in the young of all the four species of this genus, 
Which I have had an opportunity of examining, gradually fades 
* In the bserve another extreme in this system of tubes, every 
scale from eee deitig verated by a tube, as the lateral line alone shows 
GHEE in moet fishes: 2, other tahea, & ‘yptosus, have sti 
arrangem te ides the perforations of the scales of the lateral line, 
there are in this fish, ai rows of eee holes above and below the lateral li 
and alo the base dorsal, and below the insertion of the pectoral, all of 
— ch converge towards the upper angle ofthe thoracic arch aad open int the sinus 
