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L. Agassiz on the Ichthyological Fauna of Western America, 225 
ture of heterogeneous types, and must be subdivided not only into 
genera, but even into tribes. But before expressing any opinion 
upon the closer affinities of these more restricted genera it is ad- 
visable to illustrate successively their structural characters and to 
compare them with one another. I begin wit 
Chrosomus, Raf. 
The genus Luxilus of Rafinesque embraces two different types, 
which he has himself separated as subgenera under the names of 
Chrosomus and Luzilus proper. These two types differ in so 
many structural peculiarities that I do not hesitate to consider 
them as different genera. These differences are indeed so obvi- 
yet upon careful comparison such ditferences are observed between 
them, that no doubt can remain respecting the propriety of con- 
sidering them as distinct genera, if structural peculiarities are at 
all indicative of generic differences. In the first place Phoxinus 
488 two rows of pharyngeal teeth, the onter, numbering four or 
five teeth, the inner, one or two, whilst Chrosomus has only one 
tow of five teeth. Moreover, in Phoxinus the point of the teeth 
8 strongly hooked, and their inner margin entire, while in Chro- 
Somus that margin is flattened into a grinding surface, the teet 
terminating however with a small hook. 
. yprinus Smithii of Dr. now 
si Jor ee Ye om ova ree St Cee Since ling 
else but our common Hyodon. 
__ Stooxp Sznres, Vol. XIX, No, 56—March, 1855. sg 
