LL. Agassiz on the Ichthyological Fauna of Western America. 95 
Thus far, America has not been known to produce any repre- 
sentation of this type. I for the first time called the attention of 
Naturalists to its existence in our waters in my “Notice of a cel- 
lection of fishes from the southern beud of the Tennessee River,”’* 
but the scanty materials | had then in my possession did net allow 
ine to make a thorongh comparison between the representatives 
of the old world and those of the new, and even now Iam unable 
to extend my investigations to the Asiatic and African species 
described by Buchanan, McClellan, Sykes, Russell and Valen- 
ciennes. But even between the American and Enropean mem- 
bers of this tribe, most of which I have now before me. there are 
marked differences aud striking analogies. In the first lace, I 
would remark that the genus Exoglossum of Rafinesqne, which 
is entirely peculiar to North America, thongh placed near Catos- 
tomus by ail ichthyologists who have had an opportunity of ex- 
amining it, in reality belongs to the tribe of Chondrestoma, the 
very peculiar shape of its mouth being only the extreme of the 
feature characteristic of that genus and arising from the redne- 
tion and discontinuity of the lower lip near the symphysis of the 
two branches of the lower jaw and the great projection of the 
symphysis itself. The pharyngeal teeth moreover have no re- 
sembiance to those of Catostomus, either in their form or in their 
arrangement, but approximate closely the common type of Leu- 
sum, contains also exclusively American species, next deserves to 
be noticed here. Since Rafinesque, Dr. Kirtland seems to be the 
only ichthyologist, who has observed the type upon which this 
genus was founded. We find an excellent figure of it, accom- 
panying his paper upon the fishes of the Ohio and its tribntaries, 
published in the 3d vol. of the. Boston Journal of Natural History. 
lhis genus seems at first to resemble more the type of Leuciseus 
than that of Chondrostoma by its general form, and yet the at- 
tenuated, sharp, somewhat truncated lower lip, and the thickened 
snout leaves no doubt as to its real affinity with Chondrostoma. 
The fish described by Dr. Kirtland as Exoglossum dubium, of 
which Valenciennes’ Exoglossum spinicephalum is the male in the 
Spawning season, is another representative of this tribe, still more 
approximating the European -genus Chondrostoma, but differing 
rom it, in having only four pharyngeal teeth on each side, in- 
Stead of six, and which I shall call Campostoma. Finally, among 
the fishes collected by the U. S. Exploring Expedition, under the 
command of Capt. Wilkes, there is a species found in the Colum- 
bia iver, coming nearer to Heckel’s genus Chondrorhynchns, 
than to my Chondrostoma, which however constitutes another 
Senus peculiar to the Pacific slope of North America, which I 
shall call Acrocheilus. 
* Printed in this Journal, vol. xvii, 2d ser. p. 357. 
