Mr. Lesueur has published, in the 5th Number of the Journal of the Academy of Sciences of Philadelphia, for September, 1817, the description of a new fish, which he calls _Cyprinus maxillingua_: he considers it as a very singular and anomalous species, owing to the peculiar structure of its lobed lower jaw and tongue, which is external, and situated as an appendage to the former. It was discovered in Pipe-creek, Maryland, in June, 1816, by said author, who confesses that he does not consider it as properly belonging to the genus _Cyprinus_, and presumes that when other species shall be discovered, possessing the same character, they will constitute a separate genus. Although this principle and presumption is correct, it was wrong to delay the formation of such a distinct genus, because only a species was then known, since so many genera are composed of single species. However, Mr. Lesueur's expectation was verified even before he wrote it, since in May, 1817, I had discovered in the Fishkill, State of New-York, another, species, evidently congenerous with the _Cyprinus maxillingua_, having the same structure of the mouth, &c. I therefore venture to establish a separate genus for those two species, having no doubt that many more will hereafter be added to it by accurate observers, and I give to it the name of _Exoglossum_, meaning _outside tongue_. It will belong to the same natural order and family of the genera _Cyprinus_, _Catostomus_, &c. EXOGLOSSUM. _Generic Definition._--Body oblong, thick, and scaly; head without scales, mouth without lips or teeth, upper jaw longer, entire; the lower trilobed, middle lobe longer, performing the office of tongue; dorsal fin opposite to the abdominal fins; three rays to the branchial membrane. _Remarks._ Besides the above characters, the two species known at present have, in common, the lateral line ascending upwards at the base, the tail forked, &c. 1. Species. _Exoglossum vittatum_, Raf. _Cyprinus maxillingua_, Lesueur. _Specific Definition._--Back brownish olive; sides blue, with a brownish band; a black spot at the base of the caudal fin, lower parts silvery gray; lateral line ascending upwards at the base; dorsal and anal fins with nine rays; tail forked. _Remarks._ Length four inches; vulgar name _little sucker_. For further particulars, see Lesueur's description, p. 85. cum. ic. I have been obliged to change the specific name of _maxillingua_, since it has the same meaning as the generic name. 2. Species. _Exoglossum annulatum_, Raf. Head black above, cheeks and gills olivaceous, back blackish olive, sides olivaceous, lower parts olive gray; a black ring at the base of the tail; lateral line ascending upwards at the base, tail forked, dorsal and anal fins with nine rays. _Remarks._ Length from three to six inches; vulgar name, _Black chub_. Head broad and flat above, iris large and gray; fins olivaceous, abdominal distant and with nine rays, pectoral with fifteen, caudal with twenty-four.