Psenes leucurus, _Cuv. et Val._? Hist. des Poiss. tom. ix. p. 197.
Mr. Darwin’s collection contains two individuals of a species of
_Psenes_, in reference to which his notes state that they were taken in
Lat. 17° 12′ S., Long. 36° 33′ W., a hundred and twenty miles from the
nearest land above water, though shoals were considerably nearer. They
do not measure more than one inch eight lines in length; and from their
small size, and their not being in a very firm state of preservation, it
is hardly possible to say whether they are new or not. In form, they
differ but little from the _P. cyanophrys_ of Cuvier and Valenciennes:
still they are evidently not that species, and one point of difference
consists in the lateral line, which terminates beneath the end of the
second dorsal, and is not carried on to the caudal, as represented in
the figure of the above species in the “Histoire des Poissons:” the eye
too appears rather larger; the forehead is hardly so much elevated, and
the pectorals are shorter than the head. Perhaps it may be the _P.
leucurus_ of the above authors; though this species is from the Indian
seas, so that its range must be considerable if the same. The
description of the _P. leucurus_ in the “Histoire des Poissons” is too
short to determine this point. It is said to have been so named on
account of its whitish tail, all the other fins being black. In the
present species, the fins are likewise black, or at least dusky, except
the caudal, which Mr. Darwin’s notes, taken from the recent fish, state
to have had “a pink tinge.” In the same notes it is added,—“belly
silvery white mottled with brownish black; sides bluish with dusky
greenish markings; iris yellow, with dark blue pupil.” The fin-ray
formula is as follows: