in breadth, of a milk-white colour, subpellucid, subcylindrical, contractile like a worm, soft, without limbs or processes; but when magnified, the margins appear crenulate, from the skin being drawn into circular wrinkles. The anterior extremity is truncate, with a sort of thickened wart at each side. The mouth is inferior (not terminal), forming a longitudinal slit, from which there is occasionally

No. XLIX.-Udonella Caligorum.

a. Natural size, attached to a portion of the caudal filament of the Caligus. b. The same magnified.

c. A single specimen compressed between plates of glass, and highly magnified; the proboscis is thrust out of the mouth and forwards.

d. A cluster of ovaries magnified.

extruded a very short thick proboscis plaited round the rim, but edentulous; and the sucker at the posterior extremity is circular, cupped, and plain. If the body is now slightly compressed between plates of glass, we perceive near the middle a clear circular spot or viscus, containing translucid granules, and immediately under this there is another bag or viscus, about twice the size of the former. The largest appears to be the stomach; and the intestine is seen obscurely to form numerous convolutions in the space between it and the sucker; but their particular course and termination could not be traced with any degree of accuracy. Half-way between the mouth and the first circular spot, there is an opake irregular mark, which gives origin to the ovary, and which can be easily seen attached to a vesigle in this spot, by its thread-like twisted pedicle. I have never seen more than one of these in the same body, and I have seen it extruded through an aperture at the side of, or near the mouth, as is shown in two of the individuals figured. The ovaries are oval or pear-shaped, and are filled with a granular matter; they are attached in clusters to the body of the Caligus by their pedicles, and may usually be found in great numbers.

10

Malacobdella grossa (page 35).

Body 1 in. long, about ths of an inch in breadth where broadest; oblong, flat, soft, exannulose, roughish, with little granulations, and of a uniform flesh

No. L.-Malacobdella grossa.

b

a. Upper side. b. Under side.

colour. On the upper side a small vessel is seen distinctly running down the middle of the body, having a tortuous course, and terminating near the sucker; and it lies over a much larger intestine, following the same direction, and alone visible on the ventral aspect. The anterior extremity is rounded, somewhat raised above the mouth, which is placed in a sinus here, and opens chiefly on the under side; it is wide, edentulous; but, when opened, the inner surface appears flocculent, being clothed with longish papillæ, which are arranged in close longitudinal series, and cover the whole intestinal canal. This organ is nearly of uniform width and structure throughout; but the papillæ appear to be longer towards its termination, which is by a small aperture on the back, just above the sucker. The dorsal vessel begins in a sort of swelling above the mouth; and, after it has passed beyond the middle of the body, it becomes sensibly attenuated. It is not fibrous, and, indeed, exhibits no marked structure beyond a very fine and faint reticulation of the surface when exposed under a high magnifier. The space between the intestine and margins of the body is compactly filled with myriads of oviform bodies, which seem to lie, without any particular order, in a gelatinous fluid: they are roundish, opake, and encircled with a rim or pellicle of transparent jelly.

I have twice found this leech in specimens of Cyprina islandica dredged up in Berwick Bay. They were lurking between the cloak and branchiæ, and doubtless had sought out the site for a less harmless purpose than shelter from foes; but, so far as I could judge from external appearances, the oyster had not suffered any material injury.

On the suggestion of Lamarck, it has been here considered a species of Phylline; but it will not correspond with the character of the genus, for the large terminal disk or sucker is not armed with hooks, as Lamarck's definition expresses, but is quite smooth. Nor has the skin the slightest appearance of circular rings, or rugæ, even when contracted and hardened by spirits; and its whole anatomy is so unlike that of Annelides, and more especially of the true leeches, that it strengthens an opinion of Lamarck's, of there being a class of animals, yet unestablished, between the Annelides and the worms.

Malacobdella Valenciennæi (page 35).

I have seen a specimen taken in Mya truncata, from the Firth of Forth, by Dr. P. W. Maclagan; but, confounding it with the preceding, I made no description. Neither did Blainville discriminate them. He says it is 10-12 lines long by 5-6 in breadth; and the intestinal canal was much less wavy than it is represented to be by Müller in M. grossa.

The following is a translation of Blanchard's description :-"This animal is about 4 centimetres in length, and, at the middle, it is from 8 to 10 millimetres in breadth. The colour of the skin is yellowishwhite, semitransparent, permitting the intestinal canal to be seen, the colour of which, beyond the oesophagus, is ochre-yellow. The dorsal vessel is distinguished by its whiteness on this coloured intestine; and the cerebral ganglions, of a yellowish tint, are also distinguishable through the integuments. The oral aperture is a simple triangular fissure. The anus is round. The sucker is very large, thin, and flattened."

Pontobdella muricata (page 39).

"The firm adhesion of the sucker to the skin of its prey must render this animal a cruel and inveterate enemy."-Dalyell.

Their

This leech has always appeared to us a sluggish animal, lying at the bottom of the containing vessel as if it were half-dead, and contracted into an imperfect semicircle*. But Sir J. G. Dalyell, who was remarkably careful of his specimens to keep them in a living condition, found that, although torpid in solitary confinement, it raised itself to activity on the introduction of a companion. necks are intertwined, considerable activity is displayed, and one or more milk-white vesicles, resembling minute grains of oats in figure, are seen protruding from the neck or its vicinity. Some observers have represented a leech, apparently the muricata, with horns. Have they been deceived by the vesicles?"

Pontobdella verrucata (page 40).

This leech is from 4 to 6 inches in length, and about as thick as a man's little finger. Specimens preserved in spirits are of a creamyellow colour, with a dusky shade; but the animal is blackish-green when alive. The suckers are large, thick, and muscular. There are generally six tubercles on the rim of the oral one, but these are

"During the day this singular leech reposes in absolute quiescence, but towards evening, its wonted coil relaxes in wider curves, and it rears itself erect on the plane of position, with the head turned inwards. The quiescence of a solitary specimen, however, is interrupted by the introduction of stranger leeches of its own kind; their society is evidently gratifying. Five having been collected in the same vessel, all began to intertwine their necks together after fixing the sucker; they stretched and curved, or contracted the body, yet without shifting from their respective spots of adhesion. Such movements continued for hours." -Dalyell.

not always present; and the outer surface is either rugose or smooth. Moquin-Tandon says that in P. verrucata the separating ring is broader than those of the sets, and gives this as a part of the specific character; but this is not the case in my specimen. However, in P. verrucata the division into sets is more obvious than in P. muricata. The breadth of the rings varies according to the conditions under which the leech has died, and affords no character. The form of the papillæ seems alone to distinguish the species. In P. muricata they are prominent, rigid, and pointed, with the apex rougbish with spinules; in P. verrucata they are much less elevated, with a broad shield-like base, and a papilla in the centre; and they are less crowded than in P. muricata. The difference does not seem to be specifical, and hence I include both species in these observations. There is no very perceptible difference between the dorsal and ventral surfaces.

The observations of Dalyell are much in favour of the opinion that there is only one species. It lays its ova within stalked capsules which are attached to old shells, &c., and usually in groups. "The capsule consists of a sole, a short stalk surmounted by a spheroid, with a distinct umbo on the side. The capsule altogether is about three lines, and the spheroid which contains the embryo, or leech, about two in diameter. Such capsules are firmly agglutinated by the sole to the substance whereon they are deposited. They are originally white, or of the faintest carnation, of a fine soft downy aspect, with the neck orange or yellowish. They darken gradually from the time of production, and in four or five days the original white is converted to olive-green, or dull wax-yellow. They are produced singly, free of all gelatinous matter."-(p. 6.)

"The capsule consists of a coriaceous, tough, thick integument full of tenacious, albuminous, brownish matter. It contains only a single embryo, which penetrates the lateral umbo in issuing forth to the light. Then the young animal is about an inch in length."(p. 7.)

It deposits the capsules chiefly during summer.

Pontobdella lævis (page 41).

Hab. "Obtained alive in April 1838, either at Portpatrick or Donaghadee, by Capt. Fayrer, R.N., who commanded the mail steampackets between these ports."-W. Thompson.

'Corps en longue massue, très-atténué en avant, et se renflant peu à peu jusque tout après de l'extrémité postérieure, lisse, et même sans articulations distinctes; ventouses terminales: la postérieure fort petite; l'antérieure assez peu considérable, sans traces de verrues tentaculaires, ni de points pseudo-oculaires; orifices des organes de la génération très-antérieurs, au premier sixième environ; anus fort petit; couleur d'un brun roussâtre."-Blainville. To this description Blainville adds that his specimen was given to him by M. Paretto of Genoa. It was, although preserved in spirits, upwards of half a

foot in length; and, as it had altered a little, the colour and the entire smoothness of the species cannot be positively affirmed. But Mr. Thompson's specimen, on which no alteration seems to have been produced, was smooth all over the surface. It was 4 inches in length.

Pennant, in his description of the Basking Shark, says, "The fishers often observe on them a sort of leech of a reddish colour, and about 2 feet long, but which falls off when the fish is brought to the surface of the water, and leaves a white mark on the skin.”—Brit. Zool. iii. 139.

Pontobdella campanulata (page 42).

"Length, when extended, 13 lines; body round; diameter about half a line. The anterior extremity dilates as a very broad disk, somewhat like a flattened hand-bell; the posterior extremity dilates in the same manner; sucker very large proportionably. Colour of the body dark olive, finely speckled with yellow. Disk and sucker very pale."-Dalyell, p. 12. Extremely restless.

Pontobdella littoralis (page 42).

Body one inch in length and a line in diameter, slightly tapered forwards, terminated at each end with a plain circular sucker, of a uniform chestnut-brown colour, or red and mottled (for the colour varies according to the intestinal contents), smooth, rather soft and compressed in extension; the margins minutely crenulate under a magnifier.

The segments are very obscurely marked, but they are divided by circular lines which make the body appear crenulate under the magnifier. The sexual pores are near the outer extremity, and a little protuberant.

PLATE II. C. fig. 4. P. marina, of the natural size. 5. The same magnified. 6. An outline figure drawn from an individual which had the genital organs extruded.

Hirudo vittata.- Length above 2 inches; breadth 3 lines; thickness 1 line; body flattened, smooth upper surface, slightly convex. Anterior extremity formed as a cup, occasionally flattening, and applying like a disk to other substances; posterior extremity broad, thin, and large in proportion to the animal, employed as a sucker. That of a very large specimen of the Hirudo vittata, one extending 8 or 9 inches, was of smaller diameter. The body is chiefly whitish and speckled, somewhat transparent, so as to expose ten pairs of cells within. Ten projections, like hemispherical blisters, border each side of the animal, rising and falling as if by respiration; no eyes could be found.-It generally remains erect on the broad or adhering sucker, often waving to and fro."-Dalyell, p. 9.

The capsules are sessile, nearly hemispherical, about one-third of