Venericardia he considers as differing but little from Cardita, and he observes that both the one and the other approach Cardium in general form and the direction of the ribs (côtes). He states his suspicions that this is the place for Crassatella.

This family is placed by Cuvier between the Ostraces and the Camacées.

The genus Pinna is placed by this zoologist between Avicula and Arca.

Lamarck characterised his Mytilacées as having the hinge with a sub-internal, marginal, linear, very entire ligament, occupying a great part of the anterior border, and the shell rarely foliated. In this family lie places the genera Modiola, Mytilus, and Pinna.

M. Deshayes, in the last edition of Lamarck's work, allows that nearly all conchologists have admitted the family of Mytilaceans or Mytilidae, either as it was constituted by Lamarck, or after having made it undergo some modifications of little importance. M. Deshayes remarks that he himself adopted it in the 'Encyclopédie,' having suppressed the genus Modiola, which, in his opinion, has not sufficient characters, and supplied its place by Avicula. But, setting aside all former opinion, M. Deshayes, in the last edition of Lamarck, enters into an examination whether the family ought to be preserved. The genus Mytilus, he observes, has always two adductor muscles, the anterior one very small, and the posterior much larger; the lobes of the mantle are united posteriorly at a single point, so that there exists but a solitary siphon for the anus. The aperture of the mouth is not papillose within. The Modiola, he continues, differ in nothing from the Mytili; their anterior muscle is indeed in some species rather larger, and the anterior extremity of the animal is a little prolonged beyond the umbones. These differences are, in his opinion, without importance, for we pass from one genus to the other by insensible gradations. In the genus Pinna we no longer find the mantle with a posterior commissure; consequently there is no anal siphon; there are two unequal muscles, and the mouth as well as the lips are covered internally with membranous papillæ. The ligament of the Mytili is external and convex, like that of the Uniones (Mulettes), &c.; that of the Pinna is very narrow, elongated over nearly the whole of the posterior border, and often covered with a delicate testaceous lamina, losing nearly all the characters of external ligaments. The Avicule have no anterior adductor muscles, but, like the Pinna, their mantle has no posterior commissure; the mouth is furnished with papilla; the ligament has none of the characters of external ligaments, but is sunk in a superficial gutter, and takes all the characters of the ligaments of the Ostraceans and other Monomyaria. If, says M. Deshayes, in conclusion, a great value is attached to the existence of the siphons and their number, it is evident that, in following the rules laid down for classification, the Mytili should be separated from the Pinna, and that we ought to constitute from them two very approximating families. Between the Pinna and the Avicule there would seem to be more analogy than between the Mytili and Pinna. Nevertheless, in this last genus there are two adductor muscles, whilst in the Avicule there is but one. Then we ought to remember that the character resting upon the number of the muscles is very important, and if we here apply that character, we shall be led to make the Aviculæ a small family separate from the Pinna.

M. de Blainville thus characterises the Mytilacea, which he places between the Margaritacea and the Arcacea or Polyodonta. The genus Avicula among the Margaritacea thus immediately precedes the Mytilacea.

Character.-Mantle adhering towards the borders, slit throughout its inferior borders, with a distinct orifice for the anus, and an indication of the branchial orifice by the more considerable thickening of its posterior borders; a canaliculated, linguiform foot, with a byssus backwards at its base; two adductor muscles, the anterior of which is very small, besides the two pair of retractor muscles of the foot.

Shell regular, equivalve, often furnished with an epidermis, or corneous, with a toothless hinge, and a linear, dorsal ligament.

The genera placed in this family by M. de Blainville are Mytilus, with its subdivisions, and Pinna.

M. Rang gives the following as the characters of the family Mytilacés:

Animal having the mantle open throughout its inferior part, and adhering towards the borders; a separate aperture

behind for the excrements, forming very rarely a tube; the foot linguiform, canaliculated, and furnished with a byssus behind.

Shell rather delicate, generally with an epidermis, or corneous, equivalve, but very inequilateral; the hinge toothless; the ligament linear; anterior muscular impression very small; the posterior one rather large.

Marine (the genus Mytilus alone presents a species which is said to live in fresh water). (Manuel, &c.)

The genera arranged by M. Rang under this family are, Mytilus, with its subdivisions, including Modiola, Lithodomus (Cuv.), and Pinna.

Mr. G. B. Sowerby (Genera), after remarking that the Linnean genus Mytilus, on account of its principal character being its want of hinge teeth, consists of several forms that are widely distinct from each other, and which have well served as the types of several Lamarckian genera, such as Avicula, Modiola, Anodon, and others, in connection with the present genus, which deservedly retains the name of Mytilus, both on account of its form* and the priority of its claim, proceeds to observe that the other genera which have been united with it, but from which it appears necessary to distinguish it, because of a certain degree of general resemblance, are Modiola and Lithodomus: from Anodon and Avicula, together with Lamarck's Meleagrina, it is, he adds, obviously distinct; whilst one character, namely, the pointed terminal umbones, serves to distinguish it from Modiola and Lithodomus.

Mr. Garner, in his paper On the Anatomy of the Lamellibranchiate Conchifera' (Zool. Trans., vol. ii.), is disposed to regard the disposition and form of the branchia and siphons as being of great use in the classification of those animals; and he instances Anomia, Pecten, Arca, Modiola, Unio, &c., &c., as each having a particular disposition of the branchia, sac of the mantle, valves, siphons, &c., giving rise to particular modifications of the course of the aërating currents of water to the branchia. He observes that in the genera, some of which are above mentioned, no complete division of the sac of the mantle exists, while in Solen Hiatella, Pholas, &c., a different disposition takes place. With regard to the Excretory system, he found the oviduct distinct from the sac in Modiola, Mytilus, Lithodo mus, &c., whilst in Tellina, Cardium, Mactra, Pholas, Mya, and most others, the ova are discharged into the excretory organs. With reference to the Reproductive system, Mr. Garner remarks that the ovaries of the Lamellibranchiate Conchifera differ much in their situation: sometimes they form distinct parts, sometimes they are found in the foot, sometimes they are ramified in the mantle, which last disposition is present in Modiola, Anomia, Lithodomus, Hiatella, and the like.

The same author in his 'Anatomical Classification of the Lamellibranchiata' (loc. cit.), thus arranges the genera Mytilus, Modiola, Pinna, Lithodomus, and Unio.

Mantle with a distinct

anal orifice.

This genus is abundant on most rocky coasts, where the species are to be found moored by their coarse filamentous byssus, generally to such rocks or other submarine bodies as are exposed at some periods of the tide, where tides exist, and covered by the sea at high water. Mr. G. B. Sowerby does not think that, after being once attached, they habitually disengage themselves, though it appears to him probable that, when disengaged by the force of the sea, they may live for some time without being in any manner affixed.

M. Deshayes, in the last edition of Lamarck, thus describes the

Animal. Oval, elongated; the lobes of the mantle simple or fringed, united posteriorly in a single point so as to

shell of this Acephalan and a Mouse. The Greek word Muc is used to signify both a Mouse and a Muscle (Mytilus).

The name is supposed to refer to the fancied resemblance between the

form an anal siphon; mouth rather large, furnished with two pairs of soft palps, which are pointed and fixed by their summit only. Foot slender, cylindraceous, carrying at its base, and posteriorly to it, a silky byssus; abdominal mass moderate, and on each side a pair of branchia nearly equal; two adductor muscles, the one anterior and very small, the other posterior, large, and rounded.

Gland of the byssus, mantle, oviduct, &c. of Mytilus edulis. (Garner.) A, right lobe of the mantle; D. rectum; G, branchia; H, foot; J, posterior muscle; L, superior tube; O, heart; P, ventricle; Q, auricle; X, pericardium; b, tentacles; d, byssus; e, gland of the byssus; g, retractile muscle of the foot; h, valves of the mantle; i, oviduct; j, orifice of the excretory organ; k, internal ditto.

The species are numerous, and most of them are used as food; but they should be eaten with caution, for serious illness and even death have ensued from a meal made on

some of them. The byssus or beard, as it is popularly called, should be carefully cleared away, and they should be particularly avoided when cholera is about, or even when diarrhoea is prevalent.

Captain P. P. King, R. N. (Voyages of the Adventure and Beagle, vol. i.), mentions the Choro (Mytilus Choros of Molina) as among those shell-fish of the island of Chilóe which are more particularly deserving of notice. Speaking of this large muscle, Captain King says, 'Molina has described the choro of Concepcion, which is not at all different from that of Chilóe. It is often found seven or eight inches long. The fish is as large as a goose's egg, and of a very rich flavour; there are two kinds, one of a dark brown, and the other of a yellow colour; but the last is most esteemed. There is also another sort, much larger than the choro, yet equally delicate and good, the fish of which is as large as a swan's egg: it is called cholgua; but as the shells seem to be of the same species, I think the distinction can only be owing to size. In Febres's "Dictionary of the Chileno language," the word cholchua is rendered into Spanish by "cascara de choros blancos," or shell of the white muscle. Cholhua, or Cholgua (the letters g and h are indiscriminately used), must be a corruption; for it is now used in Chilóe to distinguish the large from the small choros. The manner in which the natives of these islands, both Indians and descendants of foreigners, cook shell-fish is very similar to that used for baking in the South Sea Islands and on some parts of the coast of New Holland. A hole is dug in the ground, in which large smooth stones are laid, and upon them a fire is kindled. When they are sufficiently heated, the ashes are cleared away, and shell-fish are heaped upon the stones, and covered first with leaves or straw, and then with earth. The fish thus baked are exceedingly tender and good; and this mode of cooking them is very superior to any other, as they retain, within the shell, all their own juiciness.'

Geographical Distribution.-Very wide. Few rocky coasts are without some of the species, which are all littoral. They are sometimes found affixed to crustaceans, shells, and corals.

*

Mytili with a smooth shell. Example, Mytilus edulis-Common Salt-water Muscle. This species is too well known to require description: the figures will show the shape of the shell, which is strong. when freed from the epidermis and polished, the under surface of the external part of the shell is exposed, and is of a deep blue. In this state it is often offered for sale at watering places. The inside of the valves is white with a dark rim.

The common edible muscle is found in extensive beds below low-water mark, and also at a greater depth. Rocks and stones between high-water and low-water marks are also covered with them. We once saw a lobster, which is now, we believe, in one of our museums, with its shell coated with them. The species is used largely as an article of food, and is considered rich and sapid by many; but it entirely disagrees with some constitutions, and, besides other derangements, has been known to cause blotches, swellings, &c. Some cases are recorded where these and other affections have been produced by eating these muscles, whilst some who have partaken from the same dish have escaped all evil consequences. These derangements have been attributed by some to the byssus, by others to the Pea-crab [PINNOTHERIANS], a little crustacean which shelters itself, especially at particular seasons, in the shell of the Muscle, and by others again to the muscle itself being in an unwholesome state or out of season. There can be little doubt that the muscle, like the oyster, and indeed like most other edible animals, is comparatively unfit for the food of man at certain periods; but that the Pea-crab has anything to do per se with the poisonous qualities of these esculents is denied by all who have written on the subject. When any symptoms of derangement occur after eating muscles, an emetic should be taken and afterwards a dose of castor-oil. Cases of this kind are however rare. Pennant remarks, that for one who is affected by eating muscles, a hundred remain uninjured. [See further, MYTILUS EDULIS.]

Particular localities are celebrated as producing this musele in perfection. 'Ne fraudentur gloriâ sua littora,' exclaims the author last quoted. I must, in justice to Lancashire, add, that the finest muscles are those called Hambleton Hookers, from a village in that county. They are taken out of the sea and placed in the river Weir, within reach of the tide, where they grow very fat and delicious.' In The Forme of Cury' (1390) is a receipt for dressing Muskels in brewet,' and also one for making 'Cawdel of Muskels.'

Small or seed pearls frequently occur in this species, and some years ago these were employed for medical purposes.

a, detached valve;-the animal in situ with byssus:-the mantle slightly contracted; b. valves conjoined;-animal as seen when the shell is partly forced open, with byssus.

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structure of the animal, that its place is between Mytilus and Anodon.

Geographical Distribution.-The author above quoted states that this form is found throughout Europe, and that America possesses individuals which approach it. (Mytilus recurvus, Rafinesque, &c.)

Dr. Vanbeneden records two recent species, Dreissena polymorpha and Dreissena Africana.

Example, Dreissena polymorpha. This appears to be the Mitylus Wolga, Chemn.; M. Chemnitzii, Fér.; M. Hagenii, De Baer; M. lineatus, Waardenburg, and M. Arca, Kickx.

Localities.-Inhabiting seas, lakes, rivers, and marshes; all these conditions seem favourable to it. Dr. Vanbeneden gives the following localities:-the Caspian Sea, the Black Sea, and the Baltic, the Danube, the Wolga, and the Rhine, where they are found in considerable quantities; the marshes of Syrmia (the Palatinate), the Canal Guillaume (Belgium), the lakes of Harlem (Holland), the Lea (our river Lea, we suppose, is meant), the Doks (the Commercial Docks, London, probably), and the neighbourhood of Edinburgh (Union Canal); so that this form extends nearly over the whole surface of Europe from lat. 43° N. to 56°; Turkey, Austria, Russia, Germany, Belgium, Holland, and England. (Vanbeneden.)

Mr. J. D. C. Sowerby appears to have been the first who noticed their introduction into the Commercial Docks, in the Thames, to which place he is of opinion that they had been probably brought in timber.

Habits, &c.-The species are found at the bottom of the water in beds, like the marine mytili, agglomerated in bunches by means of their byssus. They attach themselves to stones, to piles, to other shells (Unio and Anodon), and all the bodies which are in their neighbourhood. Dr. Vanbeneden remarks, in continuation, that they probably often adhere to the keels of boats, and that it is perhaps by such means that they are dispersed over such a considerable extent.

1, Auimal of uat. size,' showing the siphon exserted, and the aperture which corresponds with the auus open; view of the back. a, The siphon; b, the posterior row of papillæ; c, anal aperture. 2, View of the ventral side. a, The siphon; b, the anterior row of papilla; 3, Animal in the left valve. a, The abdomen; b, the languette in situ; c,

c, the languette.

the branchine; d, the aperture which gives issue to the excrements; e, aper

ture of the byssus; f, the byssus. (Vanbeneden.)

MYT

vol. iii. (1835), allows that the animal does not entirely nearly throughout its circumference, and only have the lobes resemble the marine mytili, which have the mantle open united posteriorly in a single point, so as to form over against the anus a small canal for the issue of the excrethe Mytilus polymorphus having two posterior apertures ments. The principal difference, he remarks, consists in prolonging itself into a short siphon destined to conduct the instead of one; the second aperture, larger than the other, water over the branchia. With regard to the other parts, he observes that they do not differ from the other mytili marine species. Thus the retractor of the foot is here less except by gradations similar to those which are found in the divided, and leaves only a single narrow and isolated impression on the valves. M. Deshayes states that he knows an analogous disposition in the marine species. The form of the foot, the position of the byssus, the form of the mouth and of the labial palps, and the interior disposition of those organs, resemble the same parts in the mytili. Some slight differences may perhaps be found in the distribution of the nerves; but M. Deshayes inquires whether it is clearly made out that this distribution does not vary as much in the marine muscles, He then adverts to the small transverse septum in each valve, the external surface of the valves, and he allows that if this character was only of which gives attachment to the anterior adductor muscle to be found in this species, coexisting with two posterior apertures in the mantle, a small generic group might be marine species, Mytilus bilocularis, for example, offer the founded on this type; but he proceeds to state that many same character, which loses its importance when we find it established by degrees, commencing in some species so as to be scarcely perceptible, increasing in others, and showing itself in its greatest development in the species last quoted Unfortunately, he adds, the animal of Mytilus bilocularis is not known; so that we are unable to appreciate the value of the character which it offers in common with the genus Dreissena of Dr. Vanbeneden.

Mcdiola. (Lamarck.)

M. Rang makes Modiola the third group of the genus
Mytilus. M. Deshayes, in his inquiry whether this genus
ought to be preserved, observes that the Mytili and Modiola
much resemble each other, as all admit, but they offer some
difference, the importance of which he proceeds to test. Of
the animals he says nothing, their analogy being so perfect,
and all their characters, internal as well as external, being so
similar that it is impossible to distinguish them. The habit
which certain species have of living in the stones which
they pierce has not changed their organization; and of the
justice of this remark those interested in the subject may,
he states, assure themselves by a comparison of the animals
themselves, which are abundantly spread abroad in all
seas. It is a received principle among all zoologists, he
continues, that animals having the same organization ought
to make a part of the same genus; but as there are persons
who attach considerable importance to certain characters in
the shells, it is right to reduce it to its just value. The
Modiolæ differ from the Mytili in not having pointed and
terminal umbones. On assembling a great number of living
and fossil species of both genera, some will be observed
whose umbones, nearly terminal, are overpassed by a small
from the Mytili to the Modiola without the possibility of
very short border; others in which this border is a little
more extended; and so one passes by insensible degrees
determining the point where one genus ends and the other
served, and then, concludes M. Deshayes, the observer will
begins. If the same comparison is continued between the
Modiola and the Lithodomi the same passage may be ob-
be convinced, as we are, of the inutility of these genera.

Mr. G. B. Sowerby, in whose Genera, No. xxvi., will be
found very instructive figures showing the variety of form
to which the Modiola, treated by him as a distinct genus,
are subject, admits that the most important character which
serves to distinguish Modiola from Mytilus consists in the
smaller side of the former advancing before the umbones,
and giving the shell a rounded termination anteriorly. In
every other respect he admits that it resembles Mytilus.
nection with other genera that are exceedingly distinct.
to which it was united in most of the older books, in con-
tinuation, and many other genera, affix themselves to
submarine productions by means of a bundle of rather
'The Modiola, like the Mytili,' says Mr. Sowerby, in con-
coarse fibres, commonly called a byssus, each fibre of which

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