Habitat, Valparaiso.
This species was found by Mr. Darwin at Valparaiso in fresh water, in
the month of August. It would seem to be nearly allied to the _A.
laticlavia_ of Cuvier and Valenciennes, brought from the same locality
by M. D’Orbigny; but, judging from the short description in the
“Histoire des Poissons,” it is more elongated, and has the head longer
in relation to the depth of the body; also has the silver band narrower.
In the _A. laticlavia_, the head is said to be equal to the depth, and
to be contained six times in the entire length; the breadth of the
silver band to be greater than in any other species. In the _A.
microlepidota_, the depth is one-eighth and the head one-sixth of the
length: the silver band not broader than in the _A. argentinensis_ and
some others. The colouring also of the fins appears different in the two
species.