96 L: Agassiz on the Ichthyological Fauna of Western America. 
It appears thus that far from being deficient in representatives 
of the tribe of Chondrostomi, North America has a greater num- 
ber of them and more diversified ones than Europe, belonging to 
four distinct genera: Exoglossum, Raf., Pimephales, Raf, Cam- 
postoma, Agass., and Acrocheilus, Agass.; to which must be added 
two other new genera to be described hereafter, founded also upon 
North American species: Hybognathus, Agass., and Hyborhyn- 
chus, Agass.- I am unable to say whether the genus Cochlogna- 
thus, B. and G., belongs to this tribe or not, as I have had no 
opportunity of examining it 
seahcitas Agass. 
The type of this genus has a general resemblance to the type 
of my genus Chondrostoma, inasmuch as the mouth opens trans- 
versely under the snout, and has a hard cartilaginous or rather 
horny edge. But it differs from that genus in having a solid rim 
along the upper lip similar to that upon the lower, and in the 
character of its scales, which resemble more those of the group 
of Barbus, than those of the common type of Leuciscus or Ca- 
penn 
a genus I would characterise it by the peculiar structure of 
the cava of the mouth, which in the lower jaw constitutes a 
transverse broad flat plate, very similar in appearance to the dental 
plates of Myliobates, being thicker along the outer edge and 
tapering gradually along the inneredge. This transverse plate i is 
square and cut at right angles externally towards the symphysis 
of the two jaws. In consequence of this peculiar structure of 
the margin of the mouth and its armature, the lower jaw is as it 
were cnt transversely, and has in no degree the rounded outline 
about the symphysis of its branches which is observed in most 
Cyprinide. ‘The membranous fold which extends from the sub- 
operculum along the interoperculum towards the symphysis of 
the lower jaw is limited by a deep furrow which terminates some- 
what behind the horny plate of the lower jaw. Along the inner 
edge of the intermaxillary bone there is a similar transverse bony 
plate which is, however, much narrower and rounded, folding 
over that of the lower jaw when the mouth is shut. Sideways 
and above, the intermaxillaries are surrounded by a fleshy lip 
which is bent forwards at the angle of the mouth to unite with 
the edge of the horny plate of the lower jaw. The upper max- 
illary bone forms a slight projection behind the angle of the 
mouth in a depression arising from a membranous fold upon the 
sides of the lower jaw, and below and behind the first suborbital 
bone. There is not the slightest rudiment of a tentacle in the 
angle between the lower termination of the intermaxillary and 
upper maxillary. But what is particularly striking in the struc- 
ture of this’ fish i is the circumstance that the horny covering en- 
