length, the lobes equal. Ventrals more forward than in the other species, decidedly in advance
of the dorsal, and attached at one-third of the entire len gth ; their axillary scale very small.
Pectorals narrow, roacliing beyond them. N o long folds of skin accompanying the rays of the
vertical fins.
C o l o u r .—N ot noticed in the recent state, in which, judging from its appearance in sph-it, it was
probably silvery, or perhaps golden, with somewhat of an olivaceous hue becoming deeper on
the back. There are evident remains of a bright longitudinal lateral band : also of a black spot
at the base o f the caudal. The dorsal and the anterior portion of the anal incline to d u sk y :
the pectorals and ventrals are slightly dusky at their extrem ities; there is also a large irregular
dusky stain on the back and shoulders anterior to the dorsal fin.
A second specimen differs from the above in being a trifle smaller, and not quite so deep in
the body. T he anal is also decidedly scabrous, as in the T. scabripinnis, and has one ray less in
it. T he colours are similar, excepting that the fins are rather less dusky, and the large dusky
stain on the back and shoulders is wanting.
Habitat, Maldonado.
This species is one of several that were taken by Mr. Darwin at Maldonado,
in tlie lake that had been suddenly drained, before alluded to. It is immediately
distinguished from all the others in this genus above described, by its small mouth
and abbreviated lateral line. The circumstance of the anal fin being scabrous in
only one of the specimens leads to the suspicion that this may be a sexual character,
perhaps common to this and several species; and, judging from its somewhat
less depth, I conceive the specimen so distinguished in this instance to be a male.
H y d r o c y o n h e p s e t u s . C u v .
Ilydrocyon hepsetus, Cuv. Reg. An. (ed. 2) tom. ii. p. 312.
------------- falcatus, Freycinet, (Voyage) Zoologie, p. 221, pi. 48. fig. 2.
F o rm .— Back rising slightly from the nape, whence the profile in front falls obliquely in nearly a
straight line to the mouth. D epth 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. T he length of the head equals the depth of the body. Snout appears rather
pointed when the jaws are s h u t; 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 orb it; 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 m outh is s h u t; 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 o f 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 b u t regular curve, with
scarcely any salient angle.
H ead 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. A bout 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 tbe depth. Scales on the lateral line not larger than the
others.
T he 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 o f the dorsal ; the first
part of this fin as high as the dorsal, but tho rays, beyond the fifth, gradually decreasing ; three
spines, the first two very m inute ; 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 term inating portion of the gill-fiap, 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.
C o l o u r .— “ Bluish silvery.”—D .— Some appearance of a dusky spot at the base o f the caudal prolonged
in a line along the middle rays, but scarcely any trace o f a hum eral one. T he dorsal
and anal incline a little to dusky.
Taken at Maldonado, in a fresh-water lake, in June. I hare scarcely any
doubt of its being the U . fa lca tu s of the Zoology of Freycinet’s voyage, the figure
of which it exactly reseinhles, 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 .
H epsetus of D'Orbigny* appears to differ from the H . fa lca tu s of Freycinet (with
which last Cuvier associates his name of H epsetus,) in having the lateral line curving
upwards rather tlian downwards, and the caudal fascia as well as the humeral
spot more marked. The Sahno fa lca tu s o îIi\o c \i is probably distinct from both.
* Voy. dans L ’Amer. Merid. At]. Ichth. pi. 0. fig. 2.