were then indicated the small number of Ampullariæ known to those authors. Bruguière afterwards removed the species into his genus Bulimus, and Lamarck then established the genus under the name which it at present bears, without however any knowledge of the animal, and the absence of this information led him to comprehend under his genus many fossil species which have not its characters. • At present,' continues M. Deshayes, when the animal is known, and in consequence of the peculiarity of its organization many have been brought alive into Europe, we have presented to us the means of completing the characters of the genus and of rendering it more natural by the rejection of all the species which do not include all the cha- | racters, or in adding those which have been distributed among other genera. Thus it is, as we have already had occasion to observe, that the Planorbis Cornu Arietis, provided with an operculum, and the animal of which has been figured, belongs, in reality, to the genus Ampullaria. We are at a loss therefore for the motive which could determine Mr. Guilding to form the genus Ceratodes on this shell, when he had the opportunity of comparing the animal with that of Ampullaria globosa, animals in which it is impossible, judging from the figures which Mr. Guilding himself has given, to perceive generic differences.'

Before we follow M. Deshayes, as we presently shall, into an inquiry with regard to the organization of this remarkable genus, it becomes necessary to advert to the acuteness of Mr. G. B. Sowerby, who first pointed out, with all due deference to Lamarck, the true place of the Planorbis Cornu | Arietis of that zoologist, and placed it among the Ampullariæ, in its true position. (Genera, No. 4.) For this he was sharply censured by Mr. Swainson, in his interesting Zoological Illustrations (title Ampullaria Globosa,' pl. 119). Specimens however soon came to hand with the operculum, thus destroying the principal ground of Mr. Swainson's severe criticism, and the knowledge of the animal soon extinguished all doubts as to the propriety of Mr. G. B. Sowerby's opinion. (See further, LIMNEANS (Planorbis), vol. xiii., p. 499.) We deem it necessary to call the attention of the student to this, that he may not be misled by the observations of a zoologist so justly distinguished as Mr. Swainson; indeed, he himself, by the position which he has assigned to Ceratodes in his lately published treatise on 'Malacology,'* virtually negatives his former judgment. Ampullaria have been, as has been before hinted, brought to Europe alive. The first, we believe, was sent to Paris by M. Caillaud from the Nile. That naturalist, during his voyage to Meröe, collected several Egyptian Mollusca, which he distributed generously among collectors. One correspondent had been anxious for the fluviatile mollusks found in the Nile. The person employed to collect these, after having gathered a large quantity of river mollusca, among which were some living Ampullaria, put them all into a box of bran (son). This box was delayed on its road by the operation of the quarantine laws for four months, and when it reached M. Caillaud, was in such a state, from the putrefaction of the greater part of its animal contents, that he hastened to throw the whole into the water. To his no small surprise he found, a few hours after, the greater part of the Ampullaria, which had been shut up with this mass of putrefaction, quietly creeping about upon the mud. He gave many individuals to M. Deshayes, who kept them alive from four to five months. The latter zoologist remarks that, since that communication, Mr. Sowerby, in the Zoological Journal, and M. Quoy, in the Zoology of the Astrolabe, have given the figures of many other species of Ampullariæ, many of which have been brought alive to Europe. We know of no other figures of Ampullariæ in the ' Zoological Journal' than those illustrative of the Rev. Lansdown Guilding's paper above copied.

On the 29th of October, 1833, Mr. Cuming, so well known for the great additions which he has contributed to our knowledge of the Mollusca by his collections from the west, and who is now employed in the same laudable pursuit in the east, brought to Mr. Broderip a specimen of Ampullaria globosa, expressing his opinion that it might be alive. Mr. Broderip immediately placed the specimen in a deep dish with some earth at the bottom, which was covered with New River water, and set it before the fire. On the 29th the animal gave no sign; but on the 30th it came forth and soon showed tokens of vigorous life. It was afterwards removed into a globular glass vase, such as is used for gold • Ante. p. 453.

and silver fish, with a good layer of earth at the bottom. The water and earth were changed periodically, and the animal continued to live in apparently good health for many weeks. Its death was probably occasioned by the difficulty of resisting the low temperature of the long cold winter nights, where there were no stoves, in short nothing beyond the ordinary fires of a dwelling-house. The specimen is now in the museum of the Royal College of Surgeons.

M. Deshayes proceeds to observe that it became an object of inquiry how aquatic animals, unable to respire, except by means of a pectinated branchia, could remain alive so long out of the element apparently necessary to their existence. Nearly all the persons, he remarks, who occupied themselves with this phenomenon, thought that the animal on retiring into its shell carried with it a certain quantity of water, which could not escape owing to the retention of the operculum, which closes the aperture with great exactness. Others thought that the humid air carried upon the branchia was sufficient to keep up the respiratory action. Wishing to know,' continues M. Deshayes, whether there were anything in the structure of the animal which could explain the singularity, we soon perceived that the upper wall of the branchial cavity was doubled, and formed a great pouch, the aperture of which was placed backwards, above the origin of the branchia. Plunged in the water, the animal has this pouch constantly filled with the ambient liquid, and on retiring into its shell and shutting itself up under its operculum, this bag still remains filled with water, and thus furnishes the necessary materials for the function of respiration. Everything leads us to believe that this is the only cause which permits the Ampullaria, pectinibranchiated aquatic animals, to remain a long time out of the water without perishing, and this explains also how it happens that in certain lakes which are annually dry, Ampullariæ are always to be found. When the great heats approach and they plunge themselves into the mud or sand, they preserve in their branchial sacs the quantity of water necessary for them during the whole time of drought.'

This is one of those beautiful provisions which meet the naturalist everywhere. The tropical torrent and lake may yield to the dry season and burning sun, but the Ampullaria, secure in the possession of his water-bag, can afford, like the camel in the desert, to wait till the rains furnish a fresh supply, and again fill the parched channel.

Geographical Distribution of the Genus.-The rivers and lakes of warm climates. Species, some of them very large (A. Guyanensis, A. Urceus, and A. Gigas, for example), have been found in Asia, Africa, and America, especially the southern portion of the latter. Olivier (Voyage dans l'Empire Othoman, &c.) states that one is found in Lake Mareotis, in company with marine shells, but he did not succeed in obtaining the living animal. Mr. G. B. Sowerby hesitates to admit into the genus another reverse species, called by Olivier A. carinata, abundant in a neighbouring river, but which, says Mr. Sowerby, if we may judge from his representation, has a horny operculum, and should therefore rather be considered as a Paludina.

The Rev. Lansdown Guilding divides his genus Pachystoma, the second of his family Ampullariada, Paludina being the first, into two sections. The genus is characterised as being furnished with a thick, marginated, and often with a channelled lip; the operculum shelly.

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Umbilicus small: shell globose. This section comprehends Ampullariæ globosa, corrugata, and puncticulata of Swainson.

Ampullaria effusa of Swainson.

Mr. Guilding is of opinion that this species forms the transition through Ceratodes to the Planorbida, and that it is probably more allied to that genus than to Ampullaria.

The genus Ceratodes of the last-named author is characterised as having a simple lip; a horny operculum; a discoïd shell; a very large and deep umbilicus, and an evanescent columella. The sole species given by him is Ceratodes Cornu Arietis above copied.

Mr. Swainson thus defines the genus Ampullaria:-Shell giopose, rarely discoid, turbinate; spire very short; aperture oblong, pointed above, rounded below. The same author characterises the four subgenera as follows:

Ampullaria, Lam. Outer lip thin; operculum horny. Example, Ampullaria fasciata of Lamarck.

Pachylabra.* Outer lip thickened; operculum shelly. Example, P. Globosa, Sw.

Lanites, Montf. Shell reversed; the body-whorl ventricose only in the middle; outer lip generally thin. Example, Lanitest Guinaiaca. Sowerby's Manual,' f. 319. (Malacology,' 1840.)

The number of recent species recorded by M. Deshayes in his Tables is twenty-four: in the last edition of Lamarck the numbers given are twenty-seven, including Ampullariæ avellana and fragilis, of which we shall presently have occasion to speak more at large. Neither Mr. Swainson's Ampullaria globosa, Captain King's Ampullaria Cumingii, nor Mr. Lea's Ampullaria Pealiana, appears among these species. Mr. Swainson gives Helix Ampullacea, var., Gmelin, as a synonym of his A. globosa, but the former stands as a synonym for A. fasciata, Lam., in the last edition of the Animaux sans Vertèbres. Mr. Swainson considers it distinct, and quotes the description and figure of Chemnitz, who, like other authors, considered it a variety of Helix Ampullacea. The rivers of India are given as the locality, by Mr. Swainson.

Ampullaria globosa: the aperture closed by the operculum.

Some of these Ampullaria, or Apple Snails, as they have been called by collectors, are of large size, as we have already stated; and some of these are figured in Lister, Chemnitz, and Spix: there are fine specimens, some from Mr. Broderip's collection, in the British Museum.

Ampullacera. (Quoy.)

The Ampullaria avellana of Lamarck was founded on the Nerita Nux avellana of Chemnitz, and was placed by Bruguière among his Bulimi. Lamarck states that it was

said to come from New Zealand. He observes that it is fluviatile, and not marine, as Bruguière supposed it to be. Considering the state of information when Lamarck wrote, no better position could have been assigned to the shell than that in which he placed it. M. Quoy however, having had an opportunity of observing the animals of the so-called Ampullariae avellana and fragilis alive, found, to his great surprise, that they presented none of the characters of the Ampullaria. Upon further inquiry he ascertained that the anatomy of these animals constituted a particular type.

The following anatomical details are given by M. Quoy.

The foot is large, transverse, yellowish, and separated by a furrow from the head, which has the form of a hood (chapron) divided into two rounded lobes, deprived of tentacles, and supporting two very small sessile eyes on a fine yellow ground. Behind is a collar rather well-formed by the border of the mantle, which only leaves a round hole at the right side for the entrance of the air, and offers a little more

outwards the aperture of the anus upon a projecting bifur cated pedicle, as in Auricula Midas. These parts, as well as those which the shell hides, are of a deep brown. The pulmonary cavity is large, and carries upon its floor (plancher) a large follicular depuratory organ, the aperture of which is readily seen on a very short anterior pedicle: the heart is behind it, and through the black pigment with which the floor is covered, a large vein is perceptible, which comes from the collar and goes along by the side of the rectum. After having lifted the partition which sepa rates the abdomen, the oesophagus was found covered by two linear salivary glands fixed by their extremities. The stomach is not distinct, inasmuch as it leads into a globular gizzard (which is muscular and nacreous, like that of a bird), containing in its interior four small depressions or fossets. The intestine which comes out of this gizzard, after having received the canals of the liver, which envelopes it, terminates by the rectum without any apparent circumvolutions. The mouth is small and membranous. More externally is seen the exciting organ opening near the right eye, in the place where might be the tentacle of the same side. Behind it is a protractor muscle and a long tortuous canal. M. Quoy states that these parts are so delicate, that he has not been able to satisfy himself whether this canal is consequent and continuous with a similar one which is much longer, and envelopes the testicle, which is placed near the gizzard. At the right of the intromissive organ is the uterus, very convex backwards, where it receives the oviduct, which comes creeping along from the ovarium, which cuts the posterior part of the tortuosity.

Thus,' says M. Quoy, we have a mollusk breathing air although it lives in pools, possessing the two sexes united, but being, notwithstanding, an insufficient hermaphrodite. It is apathic, and comes but little out of its shell, into which it retires very far upon the slightest touch. We found it sunk in the muddy sand, under some inches of saltish water, with its aperture full of earth. It is found in great abundance in New Zealand, where it is largely eaten by the natives.'

Generic Character.-Animal spiral, globular, convex; the foot short, quadrilateral, and with a marginal anterior furrow. Head large, flattened, notched into two rounded lobes supporting two sessile eyes, without the appearance of tentacles. Pulmonary cavity limited anteriorly by a collar, and having its aperture at the right border. Mouth membranous. Both sexes united.

Shell rather thick, globular, ventricose, deeply umbilicated, aperture round or oblique, with the borders united; spire short, but projecting.

Operculum horny, delicate, but little spiral, sometimes with a heel or projection. (Quoy.)

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the most interesting that has been for a long time discoM. Deshayes adopts this genus, which he thinks one of vered. It offers in fact,' says he, an entirely novel combination of an aquatic animal pulmonated and operculated, and fills up a lacuna. It is, with reference to the aquatic pulmonata, what the Helicina are with reference to the terrestrial pulmonata; Ampullacera, then, will constitute in the system not only a genus but a family, which ought to be placed at the end of that of the aquatic pulmonata without an operculum.'

Mr. Swainson (Treatise on Malacology, 1840) changes the name to Thallicera, as not liable, like Ampullacera, to be confounded with Ampullaria. He thinks that there can be no doubt that it is allied both to the operculated Pectinbranchians by its shell and its habitat, and to the pulmonary fluviatile Limnacina by its animal.

The only species known are Ampullacera avellana, Quoy (Ampullaria avellana, Lam.); and Apullacera fragilis, Quoy (Ampullaria fragilis, Lam.). M. Deshayes refers to fig. 5, in Mr. G. B. Sowerby's plate of Paludina (Genera, No. xli.) for the last-named species.

FOSSIL PERISTOMIANS.

Paludina.-Mr. G. B. Sowerby states that the fossil species abound in a thin bed immediately above the freshwater bed at Headen Hill, and also in the Petworth marble.

M. Deshayes remarks that the number of species found in a fossil state is considerable. Those on which no doubt can be thrown belong to the tertiary beds, and are particularly abundant in the fresh-water formations. Some species, he observes, are quoted from the secondary strata, but they are, in his opinion, doubtful, it being possible to refer the casts on which they have been established as much to the genus Turbo as to the genus Paludina. Many species, he adds, have been confounded with the Cyclostomata and the Bulimi, but their extreme abundance in the places where they are met with does not permit the belief that they are terrestrial shells; and as they have besides the greater part of the characters of the Paludin, M. Deshayes has referred them to this genus, in his work on the fossil shells of the environs of Paris.

The number of fossil species recorded by the last-named author in his Tables is forty-one (tertiary). This number, as regards fossil species only, is reduced to thirteen in his last edition of Lamarck.

Paludina vivipara is noted in Mr. Mantell's Tabular Arrangement of the Organic Remains of the County of Sussex' (Geol. Trans., vol. iii., 2nd series), as occurring in the Weald clay and the Tilgate beds, and Pal. elongata from the latter locality. Both are also recorded from the Ashburnham beds (lower division of the Hastings deposits). Paludinæ carinifera, elongata, fluviorum, Sussexiensis, and two or more species, probably new,' appear in Dr. Fitton's list, in his valuable paper 'On the Strata below the Chalk' (Geol. Trans., vol. iv., 2nd series).

Ampullaria.-Mr. G. B. Sowerby states that he is not certain that any fossil species of this genus exists: several, he adds, are mentioned by Lamarck, in the Annales du Museum,' among the fossil shells of the environs of Paris; others, which are thought to be genuine, are found in the London clay at Hordwell, and in the mixed stratum between the two fresh-water beds at Headen Hill, in the Isle of Wight. (Genera.)

M. Deshayes is of opinion that many fossil species given as Naticæ, ought to find a place among the Ampullariæ; whilst others, such as Ampullaria avellana, for example, ought to constitute a new genus, or should be referred to the Natica, whose characters they possess. If,' says M. Deshayes, we compare the shells of the Ampullarice with those of the Natica, we perceive differences, not only because in the Natica the shell is polished and without an epidermis, but also because the incidence of the aperture on the longitudinal axis is different in the two genera. Nevertheless we must not attach too great importance to this character, for we have actually before us a species of Natica from Terre-Neuve,' which M. Petit de la Saussaye sent us it has the form of an Ampullaria, its shell is delicate, and has an epidermis, its umbilicus is without a callosity, and, notwithstanding its horny operculum, is entirely that of the Natica. The animal itself does not differ essentially from the other Naticæ, except in the amplitude of the foot, and in the mantle.'

M. Deshayes goes on to state that up to the time when he wrote (1838) there have hardly been found any fossil species of Ampullaria about which there is not some doubt. Those shells which he has retained in the genus, from the oharacter of the aperture and the small thickness of the shell, are, he says, never met with except in marine formations, and one may always suspect that the animals which produced them were different from those of the Ampullaria properly so called. As these species have the characters of Ampullaria, and we have no means of ascertaining the analogy of the animals, we are obliged to have recourse to the characters of the shells and to determine from them alone. But a little time since, he remarks, the belief was general that fossil Ampullariæ belonged exclusively to the tertiary beds; but it is now known that this genus occurs through all the terrains de sediment,' for Mr. Sowerby has recorded a fine species in the transition beds, and M. Deshayes says that he knows many others in the oolitic series, and even in the lower chalk. (Last edition of Lamarck.) The number of fossil species recorded by M. Deshayes in his Tables is fourteen (tertiary). In the last edition of Lamarck the number is sixteen.

The genus occurs in the list of the fossils of Lower Styria,

given by Professor Sedgwick and Mr. Murchison, in their valuable paper On the Structure of the Eastern Alps' (Geol Trans., vol. iii., second series), and in Mr. Mantell's 'Tabular Arrangement of the Organic Remains of the County of Sussex' (ibid.).

In the last-mentioned catalogue Ampullariæ patula and sigaretina are noted from the blue clay of Bracklesham and the arenaceous limestone or sandstone of Bognor. The form also occurs with a? in the list from the chalk marl, and Ampullaria canalicuta is recorded in the same paper as occurring in the gault, or Folkstone marl.

PERISTO'MIUM, in mosses, is the ring or fringe of bristles or teeth which are seated immediately below the operculum, and close up the orifice of the seed-vessel. This organ is highly hygrometrical, and is supposed to assist in dispersing the spores, or seed-like particles by which such plants are propagated. Professor Lindley regards the fringes of the peristomium as incomplete leaves. PERITONE'UM is the membrane by which the walls of the abdominal cavity are lined, and all the abdominal organs are covered. The name is also sometimes applied to the cavity itself. The arrangement of the peritoneum is in every respect similar to that of other serous membranes [MEMBRANE], except that at the extremity of the Fallopian tube it communicates with the mucous membrane of that tube, and thus is indirectly exposed to the external air. It is the peritoneum, and the epithelium covering it, which gives to all the organs within the abdomen their peculiar shining surfaces, and which by its duplicatures forms the mesentery, omentum, and other folds by which those organs are attached to each other and to the wall of the abdomen, and through which their vessels pass. [MESENTERY; OMENTUM.]

PERITONITIS is an inflammation of the peritoneum. It may exist either as an acute or as a chronic disease. The chief symptoms of the acute form are pain, swelling, and tenderness of the abdomen, accompanied with fever and a frequent small and hard pulse. The pain in peritonitis is usually much more severe than that of any other inflammatory disease of the intestines or other abdominal organs. It is acute and cutting, and sometimes occurs in paroxysms; it is generally diffused, but occasionally it is almost confined to a single part of the abdomen; but its most distinguishing character is that it is greatly increased by pressure, so that in a severe case the patient cannot support so much as the weight of the bed-clothes, but lies on his back with his knees drawn up, and breathes quickly and lightly, moving the dia phragm as little as possible, so as to avoid the pain which its pressure would excite in the inflamed parts. The bowels in cases of peritonitis are usually, but by no means constantly, constipated; commonly also there are present nausea, vo miting, and hiccup, and almost always excessive thirst and prostration of strength. If not checked in its course, acute peritonitis usually terminates fatally in from five to ten days; the patient becoming more and more depressed, and all the symptoms regularly increasing till within a short time of death, when the pain commonly ceases, and a deceptive improvement in many of the other signs of the disease takes place.

The usual morbid effects of peritonitis are the effusion of serum with lymph or pus into the cavity of the abdomen, and adhesions of the opposite surfaces of the several organs within it. After death from acute peritonitis, the walls of the abdomen and the surfaces of the organs chiefly or alone affected, are found thickened, swollen, and vascular, covered with blotches of dilated blood-vessels, and more or less firmly adhering together by the lymph which is effused between them, and which, if the patient survives for a certain length of time, becomes vascular, and is converted into the usual tissue of adhesions or false membranes. [INFLAMMATION.]

The causes of peritonitis are various. Like other acute inflammations, it may occur after exposure to cold, or the other common excitants of disease; but it is more certainly produced by injuries of the peritoneum, as by tumours developed within the abdomen, by the obstructions which occur in strangulated hernia, and intussusception, of which it is a constant consequence, by the spreading of disease from the adjacent viscera, by heavy blows and falls on the abdomen, by penetrating wounds inflicted in operations for hernia or in other circumstances, by the passage of foreign bodies into the cavity of the abdomen, and especially by the ulcerative perforation or accidental rupture of any of the organs con