PLATE XXII. Fig. 4.
_M. viridescenti-fuscus; dorso et lateribus maculis crebris, hic et
illic confluentibus, nigris; ventre niveo; pinnarum radiis
nigro-punctatis._
B. 6; D. 10; A. 16; C. 16, &c.; P. 12; V. 7.
LONG. unc. 2. lin. 8.
FORM.—Slender and very much elongated. Body anteriorly subcylindrical,
compressed behind. Greatest depth not more than one-eighth of the
entire length: thickness about three-fourths of the depth. Head
rather depressed, about one-sixth of the entire length. Snout short
and rounded; mouth at the extremity; the gape moderate, not quite
reaching to beneath the anterior angle of the eye. Lower jaw
ascending a little to meet the upper, and, when the mouth is open,
appearing rather the longest. Intermaxillary fixed, forming the
entire margin of the upper jaw, the maxillary being behind it, and,
though of nearly equal development, not very distinct: both bones
slender. Teeth small, but sharp-pointed, rather widely apart,
arranged in a single row along the edge of the intermaxillary, and
in the lower jaw; the series above consists of about eighteen, that
below of about twenty-one: also a double longitudinal row on the
tongue, each row containing five or six teeth, the anterior ones
curved, and larger than any of those in the jaws: a similar double
row, but of minuter ones, down the middle of the vomer; none,
however, on the palatines or pharyngeans. Eyes rather large, their
diameter contained about three and a half times in the length of the
head, distant scarcely one diameter from the end of the snout. The
nostrils appear to consist of only a single aperture in front of the
eye, in the neighbourhood of which, and also above the eye, are
several large pores. The opercle and subopercle taken together
approach to an oblong form, the posterior margin being straight and
nearly vertical: the subopercle is not much developed, nor very
distinct. Gill-opening very large, the membrane thick, with six
rays, deeply notched beneath, and not fastened down. The whole skin
is perfectly smooth and naked, invested with mucosity. No appearance
of any lateral line, unless a fine dark streak be so called, passing
along the middle of the sides, and dividing them into two equal
parts.
The dorsal and anal are opposite to each other, and both placed very
far back, almost at the extremity of the body. They commence in
nearly the same vertical line, a very little anterior to the
commencement of the last third of the entire length; but the anal
being longer than the dorsal, it extends nearer the caudal. The form
of these fins is much as in the genus _Cobitis_. The dorsal has the
first three rays simple, the rest branched: the anal also has the
first three simple, the first very short. Caudal about one-eighth of
the entire length, with a shallow notch, the principal rays
branched. The vent is just before the anal. The ventrals arise from
about the middle of the entire length, the distance from their
insertion to the commencement of the anal being twice their own
length. The pectorals are small, and rather narrow, equalling about
two-thirds the length of the head or hardly so much: they are
attached low down, but not quite so low as in the genus _Cobitis_.
COLOUR.—(_In spirits._) Greenish-brown, with numerous conspicuous
spots and small irregular transverse bars of black. Under a lens the
spots appear to be made up of thickly crowded black specks upon a
dark brown ground: the bars result from some of the spots being
confluent. The belly appears to have been white. The rays of all the
fins are dotted with dusky, but the membranes transparent and
colourless.
The individual described above was taken by Mr. Darwin in a fresh-water
brook, in Hardy Peninsula, Tierra del Fuego. His collection, however,
contains four other specimens found in streamlets and creeks high up the
river of Santa Cruz in Patagonia, where they are said to have been
numerous. Though these last are slightly different, they are evidently
referable to the same species: they also vary a little from each other.
Their peculiarities are as under:
The largest measures 2 inches 8 lines in length, and has the following
fin-ray formula: