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L., Agassiz on the Ichthyological Fauna of Western America. 215 
Arr. XXIL—Synopsis of the Ichthyological Fauna of the Pa- 
cific slope of North America, chiefly from the collections made 
by the U. S. Expl. Exped. under the command of Capt. 
C. Wilkes, with recent Additions and Comparisons with East- 
ern types; by L. Acassiz. 
(Continued from p. 99.) 
Exocxiossum, Raf. 
Tuus far a single species of this remarkable genus is known, 
which was first described by Lesueur, under the name of Cyp- 
rinus mavillingua in the first volume of the Journal of the Acad- 
emy of Natural Science of Philadelphia, p. 185. Lesueur how- 
ever already suspected that this species would constitute a sepa- 
rate genus, but until the discovery of another similar species he 
would content himself with referring it to the genus Cyprinus. 
His expectation of such a discovery has however not been real- 
ized, since the three species soon afterwards referred to this type 
by Rafinesque, who first introduced for it the name of Exoglos- 
Sum, and those described at a later period by Kirtland and Va- 
lenciennes do not in reality belong to it. This is another among 
the many instances which show that the importance of generic 
peculiarities does not necessarily depend upon the number of s 
cles in which they occur. Rafinesque states that he had thought 
of calling this genus Glossognathus, but that this name appear- 
ing to him rather harsh, he has proposed that of L’roglossum, 
or the sake of euphony. Valenciennes remarks that he would 
have preferred that of Glossognathus, which he had himself intro- 
duced for this genus, before he read Rafinesque’s paper. As mat- 
ters now stand, we can have no choice, the name of Exoglos- 
Sum standing by the right of priority and general acceptance.* 
Kay is certainly wrong in referring this fish to the genusrCa- 
tostomusgwith which it has no generic affinity, as I have already 
shown. In calling the typical species E'voglossum Lesueurtanum, 
Rafinesque has paid a deserved tribute to the able French natu- 
Talist who discovered this fish; but in so doing, he has acted con- 
trary to the universally acknowledged law of priority, which re~ 
qutres that specific names once established, should never be 
changed, unless they are absolutely objectionable, which is by 
no means the case in this instance. Ido therefore not hesitate 
ae goring the specific name of mavillingua, first given to this 
Valenciennes de ribes specimens from Pennsylvania. I have 
* T have intr, is and sitnilar other remarks in my paper, not merely with 
reference to hee ee consideration, but chiefly as hints to American Zoolo- 
sts, who in their writings seem not always to take sufficiently into consideration 
.J€ traditional rules which have guided Naturalists since the days of Linnzus, 
* 
