to the centre of the left valve. Adductor moderate, indistinctly composed of two elements; pallial line continuous. Sexes di

Fig. 1. Animal lying in its upper (left) valve; right mantle-lobe turned

back in front.

Fig. 2. Animal in right valve, with left mantle-lobe removed.

1, ligament; o, mouth; f, foot; u, anterior; p', posterior pedal muscles; p, p, byssus and byssal muscle; a, adductor; v, ventricle; i, rectum; g, generative organ; m, gill-suspensors; r, r, reflected gill-margins.

stinct; generative organs combined with the right mantle-lobe. Ventricle exposed, not perforated by the rectum.

There is an admirable memoir on the structure of Anomia by Dr. Lacaze-Duthiers, in the Ann. Sc. Nat. 1854, t. ii. p. 1, with figures. These and some drawings by Mr. Albany Hancock have been compared with the example here represented.

[This description differs in many particulars from that given by Mr. Clark in the British Marine Mollusca.'-J. E. G.]

Placuna placenta. Singapore.

Animal nearly symmetrical, free (or attached by a byssus when very young). Mantle quite open, its margin fringed with large and small cirri, and furnished with an inner pendent border. Adductor round, subcentral. Gills as in Anomia, their outer margins grooved. Pallial muscle reduced to two fasciculi in

Right valve with the animal, as seen on removing the left mantle-lobe. 1, ligament; c, cartilage; p, pedal muscle; f, foot; h, liver; g, generative gland; v, ventricle; a, adductor; i, rectum; b, b, branchiopallial muscles.

front of, and one behind, the adductor. Pedal muscle minute, anterior, attached to the upper (left) valve. Foot small, cylindrical, tubular (very extensile?). Lips short and wide, becoming striated inside near the gills. Generative organ and rectum attached to the right mantle-lobe. Ventricle exposed, not perforated.

It will be seen by the figures that Placuna is essentially like Anomia; both are very different from Ostrea, and more like the

Scallops. Carolia (Hemiplacuna) is a Placuna with the hinge and byssus of Anomia; Placunomia has no pedal muscle, like Placuna sella; whilst Anomia pernoides has an anterior pedal sac in each valve, as pointed out by Dr. Gray.

Anatina subrostrata. Philippines.

Mantle-margins united; no ventral orifice; pedal opening quite anterior, minute. Siphons united, thick, not entirely retractile into the shell, covered with rugose epidermis; orifices small

a, a', adductors; g, single gill; o, cavity of ossicle; 7, liver; h, palpi: the termination of the alimentary canal in the exhalent siphon is indicated by dotted lines.

(fringed?). Foot very small, compressed. Gills one on each side, long, narrow, very thick and deeply plaited, furrowed at the lower edge, not continued into the branchial siphon; dorsal border free, nearly as wide as the gill. Palpi very long, narrow, free, striated inside.

Modiolarca trapezina. Falkland Islands.

Mantle-lobes united, leaving only three small, subequal ori

a, a', adductors; p, p', pedal muscles; f, pedal opening; 7, liver; the gilltubes are distended with spawn.

fices, the interspaces with two rows of cirri; branchial opening

with a fringed border, the others plain. Anterior adductor muscle larger than the posterior. Foot with a small flat sole, crenulated at the edge, deeply grooved behind and byssiferous; pedal muscles small in front, large behind, close to the adductors. Palpi very small. Gills oblong, finely striated; the outer ones not quite so deep, furnished with a dorsal border, their free edge grooved only in the middle.

This remarkable shell, which resembles the Paleozoic Modiolopsis in the large size of the anterior adductor, is found attached by its byssus to floating weed in many parts of the Southern Ocean.

III.-Notes on some new or little-known Marine Animals.
BY PHILIP HENRY GOSSE, A.L.S.

[With two Plates.]

(Fascis II.*)

Class ARACHNIDA.

Order ACARINA.

Fam. ORIBATADÆ.

Genus HALACARUS (mihi).

Body covered above with a well-defined shield, either entire or transversely sulcated; under surface divided across the middle : rostrum head-like, consisting of a bulbous lip tapering to a point, divided longitudinally beneath, allowing the protrusion of a pair of slender filiform mandibles; palpi terminated by a fang-like unguis feet cursorious, tipped with two falcate ungues; directed two forward and two backward; thighs remote. Marine. Name from aλs, the sea, and akapi, a mite.

Sp. 1. H. rhodostigma (mihi). Plate III. figs. 1-5.

Body divided above and below; claw of palpus slender, little curved; legs nearly equal; thighs of first pair ventricose; claws of all simple; whole surface minutely punctured.

Description.-Length 2nd of an inch from anus to tip of rostrum; colour pellucid whitish, stained with pale red on the anterior half; above and below studded with punctures, which, under a high power, take the form of rosettes (whence the specific name, from pódov, a rose, and σтyun, a point), or the spots on a panther's coat (fig. 4); the punctures are conspicuous on the first thighs, but are scarcely visible on the other limbs. The

* Fasc. 1. appeared in the 'Annals' for August 1853.

haunches are moderately distant at their origin, springing from the margin of the body, the shield being notched to give them exit; the third joint of the legs is the largest, much swollen in the first pair (fig. 1); the fifth is also large, and the sixth (the terminal one) is long, but slender, tapering abruptly from the middle; the claws (fig. 5) are simple hooks, much curved, neither pectinated nor tipped with an accessory piece, but the joint from which they spring is tipped with two nearly parallel styles: the legs are equal in length.

The shield of the body above is subtruncate in front, but projects in a small medial point (fig. 2); its general form is longoval, with a transverse sulcus at the origin of the second legs; this sulcus, however, does not extend across the whole breadth, being met on each side by a bent longitudinal sulcus, which cuts off a wing-like portion, on which is seated a large crescentshaped dark eye. Below, the body has two transverse divisions (fig. 1); one at the origin of the first legs, another at the origin of the third; these two impart the aspect of the division into head, thorax and abdomen, of a beetle: there is also a narrow longitudinal portion separated on each side.

The rostrum (fig. 3) forms a thick bulb tapering to a point, from which during life I observed two apparently soft, flexible, filiform, divergent organs (mandibles ?) protruded and retracted (fig. 1). At a strong shoulder on each side of the rostrum, about one-third from its point, is articulated a palpus of four joints, of which the second is by far the largest; the terminal one is a style, slightly curved, pointed, and furnished near the base with two strong bristles on the inner side, and one on the outer. All the joints of the legs are armed with a few short bristles. The vulva (fig. 1) occupies a large oval area at the hind part of the venter, and the anus is terminal.

This little species is not uncommon at Weymouth, among seaweeds from low-water-mark; and I find it in my tanks, crawling up the glass, always immersed; doubtless introduced with weedcovered stones.

Sp. 2. H. ctenopus (mihi). Plate III. figs. 6-10.

Body divided below only; claw of palpus a stout pointed hook; hind legs longest, but otherwise alike; claws of all pectinate; whole surface smooth.

Description.-Length of body to tip of rostrum nd of an inch; colour dark-red above with a white line down the centre of the back; under parts cream-white, very satiny; legs transparent-corneous. The shield of the upper parts (Pl. III. fig. 6) is entire, nearly oval, but projecting into a point over the rostrum ;