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Of a new Animal belonging to the Crustacea, discovered in the Antarctic
Seas, by the author,
Animal composed of a head, thorax,
and post-abdomen or tail, constituting in all thirteen distinct segments.
Head deeply inserted into the cephalic
segment of the thorax. Eyes sessile, and finely granulate.
Antennae two pairs, placed one above the other, with an elongate
multiarticulated filament. Mouth as in ;the ordinary Isopods;
mandibles not palpigerous; the two superior foot-jaws expanded into a
well defined lower lip, bearing palpi.
Thorax separated into seven distinct
segments, the three posterior ones biarticulate near their lateral extremities;
each segment giving origin to a pair of perfect legs, terminating with
a strong and slightly curved nail.
Post-abdomen, or tail, divided
into five segments, provided with neither styles nor swimmerets; the under
surfaces supporting a pair of brachial leaflets, longitudinally arranged,
and covered by two biarticulated plates attached to the outward edges
of the last segment, closing over them much in the manner of an ordinary
SPECIES G. ANTARICTICA. (Eights)
Animal perfectly symmetrical, ovate,
elongate, and well depressed. Teguments solid and calcareous. Color, brown
sepia. Length, from the insertion of the antennae, three and a half inches;
width, one and three quarters.
Head transversely elliptical, terminating
at its lateral and anterior corners acutely, and incurved; anterior margin
obtusely elevated, and arched each way to its centre. Superior surface
of the head ornamented with an imperfectly sculptured "fleur-de-lis;"
posterior portion obtusely elevated, producing a marginal rim. Eyes
small, reniform, indigo blue, and placed near the lateral and. anterior
portion of the head, so deeply impressed in the margin of the shell as
to be easily distinguished from beneath. Inferior pair of antennae
longer than the superior, corresponding in length to the width of the
head, transversely from spine to spine; articulations four in number;
last segment longest, the remaining three gradually diminishing in length
as they proceed to the place of insertion; segments triangulate, with
angular projections on their surfaces; edges of the angles, and articulating
extremities rigidly spined. Terminating filament about the length of the
basal articulations, gradually attenuated until it diminishes to a finely
pointed apex. Superior antennae half the length of the inferior, three-jointed,
and terminating with an attenuated filament whose articulations are indistinct;
segments angular, external one much the longest; extremities and angles
likewise spined. Mouth with the labrum or upper lip hard and massive,
resembling in form a reversed heart. The mandibles are without palpi,
stout and osseous, tipped with a hard and black enamel. The maxillae are
furnished with the usual palpi. The lower lip, or superior foot-jaws when
united, sub-cordate; its palpi five-jointed, snugly embracing the manducatory
organs along their base, like a row of ciliated leaflets.
The thorax is composed of seven distinct segments,
each one being beautifully ornamented on its superior surface by an elongated
and sub-conic insculptation, forming a series, whose pointed apices almost
unite along the longitudinal dorsal ridge. These-segments are finely bordered
along their posterior articulating edges by an elevated and continuous
marginal rim, extending to the lateral extremities of the shell. The cephalic
depression is likewise margined by an obtusely elevated border. Each segment
of the thorax gives origin, beneath, to a pair of ponderous angulated
legs, composed of the ordinary parts. The three anterior pairs project
themselves forward, and are closely compressed upon the inferior surfaces
of the three foremost segments; they are monodactyle, with the nails incurved
upon the anterior edges of the rather largely inflated penultimate joint.
Each joint is furnished at its articulating extremity with rigid spines;
the inner edges of the penultimate joint, together with those of the three
adjoining, are provided with a double row of tufted cilia, disposed diagonally,
and much resembling in appearance the arrangement of hairs in an ordinary
brush. The four posterior pairs of legs are directed backwards, strongly
triangulate, stout and ponderous, terminating by a slightly curved nail;
their length is nearly equal, but they gradually increase in thickness
as they recede toward the tail. The basal joints are large and inflated
; the remainder .regularly angulate. , The extremities of the articulating
joints, and edges of the two inferior angles, are each provided with a
series of tufted and rigid spines.
The post-abdomen is composed of five segments. The
four anterior ones are much smaller than those which constitute the thorax,
but greatly resemble them in form, being ornamented on their superior
surfaces with similar insculptations, though but slightly defined. Each
of these segments is provided beneath with a pair of articulated pedicels,
which furnish a support to the bifoliated bronchial leaflets. These leaflets
are arranged longitudinally one upon the other, and are entirely concealed
by the biarticulated plates of the caudal segment; they are sub-ovate
and elongate; the outward ones smaller than those which they cover, and
are nearly surrounded by a fringed cilia, most conspicuously developed
along their inner margins. The second pair are each supplied with an elongated
style, extending almost to the termination of the caudal segment. The
terminating segment is large and triangular, giving attachment to the
biarticulated plates at a single point on its outer margins near the base,
which enables the animal to close them together in a line along its centre
beneath. These plates are about the length of the segment, and of a triangulate
form, each one having near its termination a small oval articulation.
The segment and marginal plates are slightly inflated along their external
edges, producing an obtusely elevated border.
The segments constituting the thorax. and post-abdomen are supplied by a central, angular, and elongated knob which, when united, form a prominent dorsal ridge, gradually diminishing in its backward course, and forming a sharp elevated line along the caudal segment) terminating at its extremity in a short and obtusely pointed spine.
This beautiful crustacean furnishes to us another close approximation to the long lost family of the Trilobite. I procured them from the southern shores of the New South Shetland Islands. They inhabit the bottom of the sea, and are only to be obtained when thrown far upon the shores by the immense surges that prevail when the detached glaciers from the land precipitate themselves into the ocean.