L. Agassiz on the Ichthyological Fauna of Western America. 73 
the outline of the mouth. Their pharyngeal teeth also, as far as 
e to ascertain, have a peculiar structure. Even 
if the subdivision of the Cyprinide into genera had never been 
extended beyond the limits marked out by Cuvier, three, at least 
of the species from Oregon should be admitted as new types of 
this family, for which genera I shall propose the names of Mylo- 
cheilus, Ptychocheilus and Acrocheilus. 
TRIBE OF CATOSTOMI. 
. 
fourth of which embraces our Catostomi. This tribe is very 
natural, if we exclude from it the genus Exoglossum, the true 
affinities of which are with Chondrostoma and not with Catos- 
tomi as Heckel admits. The true Catostomi have very remarka- 
ble pharyngeal bones, with a large number of compressed teeth, 
arranged like the teeth of a comb, upon the inner prominent edge 
of these bones, and gradually increasing in size from above down- 
the te 
Heckel subdivides the family of Cyprinoids into ten tribes, the 
f 
the homology of the two becomes at once obvious. See fig. 2, 
a anda”. The pharyngeal teeth correspond to the armature 
Upon the inner curve of the branchial arches; they may, how- 
ever, be either simple epidermic serratures or papille, or assume 
the structure of genuine teeth and become soldered to the bone 
Upon which they are formed, as is the case also with the maxil- 
lary teeth of so many fishes. 
Notwithstanding the similarity of the general arrangement of 
the pharyngeal teeth in all Catostomi, there are still such differ- 
ences in their form and number, and especially in the shape of 
their inner edge, that these peculiarities afford additional evidence 
of the propriety of acknowledging several genera among them, 
most of which have already been indicated, though very indiffer- 
Srconp Series, Vol. XIX, No. 55.—Jan., 1855. 10 
