_Corpus elongatum, gracile, antice subcylindricum, postice compressum,
nudum, squamis nullis. Caput depressum. Rostrum breve, obtusum: os
terminale, rictu modico. Maxillæ debiles; superior margine ex
ossibus intermaxillaribus omnino formato, maxillaribus retroductis
et a labio partim celatis. Dentes minuti, acuti, in maxillâ utrâque
uniseriati; in linguâ et vomere biseriati; in ossibus palatinis et
pharyngalibus nulli. Apertura branchialis amplissima, membranâ
sex-racliatâ, subter gulam profundè emarginatâ, haud isthmo annexâ.
Pinnæ dorsalis et analis valde retropositæ, oppositæ. Pinnæ
pectorales et ventrales parvæ. Pinna caudalis leviter emarginata._
There can be no doubt, I imagine, as to this being an entirely new form,
and a very interesting one, from the circumstance of its being at the
extreme end of the family to which it belongs, and its very much
departing from the usual characters of that family. I have referred it
to the _Cyprinidæ_, taking that group in the enlarged view in which
Cuvier accepts it; though by those who divide it into subfamilies it
would probably be associated with the _Cobitidæ_, or made to constitute
a distinct one by itself. It agrees with the _Cyprinidæ_ in general in
the form of its mouth, in the upper jaw having its margin entirely
formed by the intermaxillary, the maxillary being present, but placed
behind and partly concealed in the thickness of the lip, and in the want
of an adipose; but it altogether departs from that family in the entire
want of scales, of which there is not even a vestige in the dried skin,
and in which respect it would seem to shew an affinity to the
_Siluridæ_. Yet it has none of the other characters of the family just
mentioned. On the other hand, in the backward position of the dorsal and
anal fins, which are opposite to each other, it agrees with the
_Esocidæ_. The pharyngeal bones are unarmed, but this deficiency is made
up for by the strong curved teeth on the tongue, independently of the
minuter ones in the jaws.
The intestine is extremely short and quite straight, measuring only
fourteen lines in length from the pylorus to the anus, in a specimen two
inches and a half long. The stomach is of an oval form, of considerable
capacity, very membranaceous, with the cardiac and pyloric openings near
together at the upper extremity, from the latter of which the intestine
is immediately reflexed to pass off to the anus. In the specimen
dissected, the stomach was much distended by a nearly perfect individual
of the genus _Colymbetes_, which appeared to have been recently
swallowed, and was scarcely at all altered. There are no cœcal
appendages. The air-bladder is of an elongated oval form, and of
considerable development.
Mr. Darwin’s collection contains no less than three species of this new
genus, differing but slightly from each other. Two are from the most
southern parts of South America, the third from New Zealand.