Hydrocyon hepsetus, _Cuv._ Reg. An. (ed. 2) tom. ii. p. 312.
———— falcatus, _Freycinet_, (Voyage) Zoologie, p. 221, pl. 48. fig. 2.
FORM.—Back rising slightly from the nape, whence the profile in front
falls obliquely in nearly a straight line to the mouth. Depth
contained about three and a half times in the length, caudal
excluded. Both head and body much compressed, the greatest thickness
being only two-fifths of the depth. The length of the head equals
the depth of the body. Snout appears rather pointed when the jaws
are shut; when open, the lower jaw is a little the longest. Gape
considerable. Maxillary long, commencing before the eyes, and
reaching to a vertical from the posterior part of the orbit;
inclining downwards, lapping obliquely in part over the lower jaw,
gradually widening towards the posterior extremity, which is rather
obliquely rounded. Intermaxillary with two sharp canines in front,
then on each side four or five very small hooked teeth, then another
large canine, though not so large as those in front; behind this
commences the maxillary, which is armed all along its margin with a
regular row of small equal hooked teeth, resembling sharp
serratures; a similar row on each palatine, but none on the vomer or
tongue; this last pointed, and free at the tip. Lower jaw with two
strong canines in front, larger than those in the upper, and fitting
into two holes above, when the mouth is shut; on each side of these
are three only half their size, but increasing backwards, placed at
rather wide intervals; then follow a row of close, minute, sharp
teeth, similar to those on the edge of the maxillary. Eyes rather
large, their diameter not quite one-fourth the length of the head,
distant one diameter and a quarter from the end of the snout.
Suborbital large, consisting of three pieces. Preopercle
rectangular. A row of pores, not very distinct, along the under part
of the lower jaw, thence continued along the limb of the preopercle.
Opercle and subopercle taken together with the posterior margin
forming a slight but regular curve, with scarcely any salient angle.
Head naked; scales on the body of moderate size, arranged in somewhat
oblique rows, especially below the lateral line; one from the middle
of the side below the lateral line of an irregularly rounded form,
the posterior margin rather sinuous, the disk with numerous fine
concentric striæ, but no deeper-cut striæ on the basal portion.
About sixteen scales in a vertical row, and fifty-seven or
fifty-eight in the lateral line: this last bending downwards in a
curve which falls below the middle of the depth. Scales on the
lateral line not larger than the others.
The dorsal answers to the space between the ventrals and anal; its
height equals the depth to the lateral line. Anal long, commencing
exactly under the last ray of the dorsal; the first part of this fin
as high as the dorsal, but the rays, beyond the fifth, gradually
decreasing; three spines, the first two very minute; the last soft
ray double. Caudal in this specimen injured. Adipose and last ray of
the anal in the same vertical line. Pectorals two-thirds the length
of the head, attached very low down beneath the terminating portion
of the gill-flap, narrow and slightly falcate, reaching to the
ventrals, which last are one-fourth shorter. A long narrow scale in
the axilla of each ventral one-third the length of the fin itself.
B. 4; D. 11; A. 3/26; C. 22, &c.; P. 12; V. 8.
Length 4 inches 3 lines.
COLOUR.—“Bluish silvery.”—D.—Some appearance of a dusky spot at the
base of the caudal prolonged in a line along the middle rays, but
scarcely any trace of a humeral one. The dorsal and anal incline a
little to dusky.
Taken at Maldonado, in a fresh-water lake, in June. I have scarcely any
doubt of its being the _H. falcatus_ of the Zoology of Freycinet’s
voyage, the figure of which it exactly resembles, excepting that the
humeral dark spot, if it ever existed, and which is not mentioned in Mr.
Darwin’s notes, is now almost entirely effaced. It is probable, however,
that there are two or three species nearly allied, for which reason I
have been the more particular in my description. The _H. Hepsetus_ of
D’Orbigny[36] appears to differ from the _H. falcatus_ of Freycinet
(with which last Cuvier associates his name of _Hepsetus_,) in having
the lateral line curving upwards rather than downwards, and the caudal
fascia as well as the humeral spot more marked. The _Salmo falcatus_ of
Bloch is probably distinct from both.