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The duty on raw silk is 1d. per lb.; on waste, knubs, and husks, 18. per cwt.; and on thrown silk the following duties are imposed:-58. 2d. per lb. on organzine and crape, and 3s on tram and singles, dyed; 3s. 6d. on organzine and crapes, 28. on tram, and 1s. 6d. on singles, not dyed. It is objected to this duty on foreign-thrown silk that it raises unnecessarily the price of all silk thrown at home. A drawback is allowed on the exportation of foreign-thrown silk: no British-thrown silk is exported. The first silk-throwing mill erected in England was at Derby, in 1718. [DERBY.]

manufacture was anything but satisfactory; the manufac
turers complaining of the smuggling of foreign silks, par-
liament vainly endeavouring to exclude them, with constant
disputes about wages on the part of the weavers. In 1773
they obtained an act, called the Spitalfields Act, which
entitled the Middlesex weavers to demand fixed wages, to
be settled by the magistrates. To this act may be attributed
the establishment of the silk manufacture in various parts
of the country; and having done great mischief, it was
repealed in 1824. The changes introduced in 1824 (some
of which only came into operation July 5th, 1826), with a
successful, as the table of the consumption of silk, be-
view of stimulating the silk manufacture, have been most
fore and after the duties were reduced, sufficiently proves.
Now that silk has become cheaper, and consequently a
of fashion than when it was an expensive luxury. The
commoner article of dress, it is less dependent on the caprice
declared value of silk goods exported since 1820 is shown
in the following table :-

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1820 to 1823 (inclusive)
1824 to 1827
1828 to 1831
1832 to 1835
1836 to 1840

:

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Annual average.
£.
369,835

286,119

405,961

693,961

771,479

Reeling from the cocoons is only performed in countries
where the silk is produced. Silk reaches the weaver in
three different states, in which it is called singles, tram, and
organzine [RIBAND], the preparation of which is the busi-
ness of the throwster. In plain silk-weaving the process is
The declared value of silk manufactures exported in 1839
much the same as in weaving woollen or linen; but the was 868,1187. of which the United States of America took
weaver is assisted by a machine for the even distribution of 410.0931.; British North America, 136,750l.; Australian
the warp, which frequently consists of eight thousand settlements, 46,7247.; France, 44,6287.; British West
separate threads in a breadth of twenty inches. The Jac- Indies, 38,4677.; Chili, 44,7337.; Brazil, 23,1177.; other
quard loom, invented by a weaver of Lyon, has been the states of Central and Southern America, 49,060.; Germany,
means of facilitating and cheapening the production of fancy 17,135.; East Indies and Ceylon, 14,7137.; Holland,
or figured silks to an extraordinary extent. Patterns which 14,3067.; Belgium, 10,3167.; all other parts, 18,1367.
required the greatest degree of skill and the most painful The value of the silk manufactures of Great Britain is
labour are produced by this machine by weavers of ordinary estimated at between 6,000,000l. and 7,000,000l. One-half
skill, and with but little more labour than that required in of the silk factories are in Cheshire, next to which stand
weaving plain silks. The Jacquard loom has been im- Lancashire, Somerset, Derbyshire, and Staffordshire. There
proved by Mr. Hughes and Mr. Jennings, but at Lyon it are one or more factories in above one-half of the counties
has undergone no alteration. The power-loom has been of England; one or two factories have been established in
only partially employed in the silk manufacture; and ex- Ireland, and a few more in Scotland. They employ alto-
cepting for the commonest goods, it does not possess any gether in these factories above 30,000 persons, of whom
great advantage over the hand-loom, as the delicacy of the two-thirds are females.
material to be worked, and the attention which must be
given to the process of the weft, frequently render it neces-
sary to stop the machine.

Brocade and damask, the most sumptuous articles of silk manufacture a century ago, are now comparatively unknown. Persian, sarsnet, gros-de-Naples, ducapes, satin, and levantines, are the names given to plain silks, which vary from one another only in texture, quality, or softness. Satin derives its lustre from the great proportion of the threads of the warp being left visible, and the piece being afterwards passed over heated cylinders. Other varieties of silk goods are produced by mechanical arrangements in the loom, such as using different shuttles with threads of various substances, &c. The pile which constitutes the peculiarity of velvet is produced by the insertion of short pieces of silk thread, which cover the surface so entirely as to conceal the interlacings of the warp and woof. The process of weaving velvet is slow, and it is paid for at five times the rate of plain silks. There are several sorts of goods in which silk is employed with woollen materials, as poplins and bombazines, The Chinese, says Mr. Davis (p. 286), make a species of washing silk, called at Canton 'ponge,' which becomes more soft as it is longer used. Their crapes have never yet been perfectly imitated; and they particularly excel in the production of damasks and flowered satins.

The silk manufacture, after its introduction into England in the fifteenth century, remained for a long period one of the least important branches of the national industry. After the revocation of the Edict of Nantes, in 1685, about 50,000 refugees fled to England, a large proportion of whom settled in Spitalfields, and carried on the siik manufacture. At this period foreign silks were freely admitted; and from 1685 to 1692, silks to the value of from 600,000l. to 700.000l. were annually imported. In 1692 the refugees obtained an exclusive patent for certain articles; and in 1697 parliament prohibited the importation of French and other silk goods; and in 1701 the silk goods of India and China were included in the prohibition. Some inconsiderable relaxation was made in this policy in 1713, but in 1765 the system of prohibition was again fully adopted, and continued in operation until 1824. During this period the state of the

The duty on silk manufactured goods imported from European countries is equivalent to 30 per cent. ad valorem. In 1839 this duty produced 227,438., and the value of the goods was therefore about 700,0007, nine-tenths of which were from France. The exportation of silk goods from France to England was 3,589,594 lbs. from 1827 to 1838; but the quantity entered at the English customhouse was only 1,875,708 lbs., and there were therefore 1,713,886 lbs. introduced by smuggling, or 48 per cent. of the total quantity entered at the French custom-house for exportation to England. The duty on the legally imported goods averaged 20s. 4d. per lb.; but if the illegal imports could have been charged also, a duty of 10s. 11d. would have produced the same revenue. (Table by G. R. Porter, Esq., of the Board of Trade, in the Report of Committee on Import Duties)

The silk manufactures of India are subject to an ad valorem duty of 20 per cent., which, in 1839, produced 19,8677. The imports consisted in that year of 503,182 pieces of bandannoes, romals, and silk handkerchiefs, of which only 112,280 paid duty for consumption in this country; and of other articles the greater part were re-exported.

(Treatise on the Silk Manufacture, in Lardner's Cyclopædia Ure's Philosophy of Manufactures; Manual for the Culture of Silk, prepared by order of the Massachusetts Legislature, Boston, 1832; Essays on American Silk, with Directions for raising Silk-worms, Philadelphia, 1830; Second Report on Commercial Relations between Great Britain and France (Silk), 1835.)

SILK-WORM. [BOMBYCIDE.]

SILLIMANITE, a crystallized silicate of alumina. It occurs in rhombic prisms imbedded in quartz. Cleavage parallel to the long diagonal. Colour dark brownish-grey or clove-brown. Fracture uneven, splintery. Specific gravity 3:41. Lustre vitreous, nearly adamantine on the face of cleavage. Nearly opaque. Hardness 8.0 to 8.5. Brittle and easily reduced to powder.

It is inet with at Saybrook, Connecticut, North America. It was at one time considered to be a variety of anthophyllite, but it is much harder than this mineral, and contains

A

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54 11 2.00 0.51-99 29

Oxide of Iron Water SI'LPHIUM (iλpiov). Antient authors mention this plant and its juice. In the article on LASER, it has been stated that two kinds are described of this substance, which | is also called juice of silphium. One kind, from Cyrene, was probably yielded by Thapsia Silphium [LASER], and the other was most likely assafoetida, which has been employed medicinally by Asiatics from very early times, though it has been known by this name in comparative modern times.

Silphium was however remarkable for other properties, and hence has attracted the attention of modern travellers who have recently visited the countries where the silphium is described as growing by the antients. The army of Alexander, in crossing the mountain-range which Arrian calls Caucasus (iii. 28, 10), and which is the same range that ne afterwards mentions under the name of Paropamisus (v. 5, 3), met with the Silphium. Arrian says, on the authority of Aristobulus, 'In this part of the Caucasus nothing grows except pines and Silphium, but the country was populous, and fed many sheep and cattle, for the sheep are very fond of the silphium. If a sheep should perceive the silphium from a distance, it runs to it, and feeds on the flower, and digs up the root and eats that also. For this reason in Cyrene they drive the sheep as far as possible from the spots where the silphium grows, and some even fence in such places to prevent the sheep from entering them, if they should approach; for the silphium is worth a good deal to the Cyrenmans.' Burnes, in crossing the Hindu Koosh, and seeing both the men and cattle eating the young parts of the assafoetida plant, supposed that it must be the silphium of Arrian. But as this author describes the country where the silphium grows as abounding in cattle, Dr. Royle had concluded that the Prangos of Mr. Moorcroft was the silphium alluded to, and which is much fed on by sheep and cattle in the present day in Tibet. Mr. Vigne, when travelling in these regions, came to the same conclusion. It is probable therefore that both plants, being umbelliferous, and employed for the same purposes in nearly the same regions, may have contributed to form the accounts which are so brief in antient authors. [LASER; PRANGOS.] SI'LURES. [BRITANNIA.]

SILURIAN SYSTEM. One considerable group of the fossiliferous primary strata, occurring in remarkable perfection in Wales, especially in the eastern and some of the southern districts, and in some of the adjoining English counties, is thus named by Mr. Murchison in a very splendid work, the fruit of his long investigation of this part of the series of British strata. Under this title we propose to arrange some general views of the present state of our knowledge regarding the history of the lower Palæozoic strata. [GEOLOGY; PRIMARY STRATA; PALEOZOIC ROCKS; SALIFEROUS SYSTEM.]

When Mr. Murchison commenced his researches in Shropshire and Wales (1831), the principal knowledge we possessed of the succession of the older stratified rocks of Britain, then commonly called grauwacké and transition formations, was based on the still incompletely published labours of Sedgwick in Wales and the district of the English lakes; and so little was known of their fossil contents, that it is believed the first definite notice of this kind was contained in Mr. Phillips's description of a group of slaterocks in the vicinity of Kirby Lonsdale. (Geol. Trans., 1827.) Now, in consequence principally of the development given to this subject by the appearance of the Silurian researches of Mr. Murchison, and other works to which it has led, we are able to trace in one consecutive history nearly the whole series of mineral depositions and organic combinations of which the ocean was antiently the theatre, from the period of the mica schists to the termination of the carboniferous æra.

In this survey, the Silurian strata form a very conspicuous and interesting portion, and in the district from which the type was originally drawn they appear within distinct and definite limits which seem to insulate them from the older and new rocks, and to justify their claim to the rank of a peculiar system; but in other districts phenomena appear

which show that the order of physical changes and organic combinations which characterise the Silurian System, was in operation both before and after the period included in the ages of the four Silurian groups of Llandeilo,' 'Caradoc,'Wenlock,' and 'Ludlow; while in other districts these characteristic assemblages do not all clearly appear; and thus we are naturally conducted to a more comprehensive view of the whole of the antient (Palæozoic) formations. Whatever be the true theory of the origin of the Granitoid Strata of gneiss and mica schist (with their many and various quartzose, chloritic, and calcareous accompaniments), it is at least certain, as a general rule, that rocks of this general type are prevalent among the very deepest and oldest deposits from water which retain proof of their watery aggregation, and that they are in this position devoid of the traces of antient life.

Equally certain is the character of the great series of Neptunian rocks which lies upon the mica schist; it is a vast and various mass of strata (principally argillaceous, locally arenaceous or conglomeritic, rarely yielding limestone), in which, though unequally, and in degrees varying with locality, slaty cleavage tends to be developed. Organic life has left traces in this series of muddy sediments both of vegetable and animal origin; in the lower and older parts very sparingly, in the upper parts abundantly. If, with Professor Sedgwick and Mr. Murchison, we take the series of these rocks as they appear in Wales and Cumberland, namelySilurian, or upper group; Cambrian, or middle group;

Cumbrian, or lower group;

we shall find in the mineral characters of these groups in the countries named, some diagnostic marks of importance, but they vanish or become equivocal in other regions. In like manner the organic contents seem, in the countries named, to be definitely arranged in zones, so as to mark successive periods there: no organic remains are known in the Cumbrian rocks; they are rare, and confined to a few layers, in the Cambrian deposits; and are very plentiful and general in the Silurian group. The districts in which these peculiarities occur are probably more wide and seattered farther asunder than those in which the original types of mineral structure prevail; but yet it is evident that they are limited in respect of geographical area, and variable in regard to the distinctness and completeness of the terms, even in districts not far removed from the centre of investigation. Let any one who may desire proof of this compare the argillaceous series of Ayrshire, Westmoreland, Pembrokeshire, Tyrone, or Waterford, in which Silurian fossils occur, with the full and varied series of Shropshire, the Berwyn, and Snowdon.

Under these circumstances of difficulty in regard to the right general view of the antient fossiliferous strata, we

must consider the series of Silurian rocks and fossils not as the type of this enormous sequence of mineral and organic phenomena, but as one, and perhaps the richest of all the local physical combinations of that antient period, and employ it as a general term of comparison for reducing to order and place many detached and difficult districts in which the strata have local, peculiar, and perhaps exceptional aspects.

Mr. Murchison arranges the Silurian strata in groups, as follows; in a descending order :

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1500

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very variable

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the old red-sandstone, often to a considerable and rather, gimyona, 1; Mesomyona, 3; Brachiopoda, 53; Gasterocontinuous escarpment, as near Usk and Ludlow. poda, 7 Monothalamacea, 3; Polythalamacea, 6; Crustacea, 8; Doubtful, 2 (in all about 95 species). Mineral Veins.-Green copper-ore (Malachite); thin strings of galena; and in the vicinity of trap true mineral veins occur.

Organic Contents.-Polypiaria, 2; Crinoidea rare; Conchifera Plagimyona rather plentiful, 10; Conchifera Mesomyona, 1; Conchifera Brachiopoda, 15; Gasteropoda, 6; Cephalopoda Monothalamacea, 3; Cephalopoda Polythalamacea, 6; Crustacea, 5; Annelida?, 1; Fishes, 7; Doubtful, 3 (in all about 58 species).

Localities.-Ludlow; vicinity of Usk.
Aymestry Limestone.

Mineral Character.-Subcrystalline, argillaceous limestone, bluish-grey, or mottled, as near Aymestry.

Structure.-Irregularly laminated, or nodular; with cross joints nearly rectangulated to the plane of stratifica

tion.

Aspect of the Country.-Often a slightly prominent terrace on the woody steep escarpment of a hill, capped with Upper Ludlow rocks, as near Ludlow.

Organic Contents.-Polypiaria, 12; Crinoidea rare; Plagimyona, 6; Mesomyona, 2; Brachiopoda, 12; Gasteropoda, 9; Monothalamacea, 1; Polythalamacea, 4; Crustacea, 3 (in all about 49 species).

Localities.-Aymestry; Sedgeley near Dudley, &c.
Lower Ludlow Rocks.

Mineral Character.-Argillaceous (called Mudstone'), light-grey, dark-grey, or black, but weathering to ashen hues, as in the Wigmore Valley.

Structure. Partially flaggy, in places the lamination is uneven and nodular. In the lower parts, nodules of black limestone in lines of stratification.

Localities.-Caer Caradoc; May Hill; near Llandeilo.
Llandeilo Flags.

Mineral Character.-Hard dark-coloured flags, some-
times slightly micaceous, frequently calcareous.
Structure. Thinly laminated, parallel to the stratifica-
tion, with some internal oblique cleavage.

Aspect of the Country.-Not characteristic, the stratification being commonly very highly inclined and the masses very thick.

Organic Contents.-Polypiaria, 4; Crinoidea rare; Plagimyona, 1; Mesomyona?; Brachiopoda, 26; Gasteropoda, 3; Monothalamacea, 1; Polythalamacea, 1; Crustacea, 11 (in all about 47 species).

Mineral Veins.-Occur in the vicinity of trap, as in the Shelve and Corndon district.

Localities.-Near Built; Llandeilo; Pembrokeshire. Pyrogenous rocks are associated with the Silurian strata in many situations-as the Caradoc Hills, where compact felspar predominates-the Wrekin and Lilleshall Hill, characterised by sienitic rocks-Corndon, full of greenstone. Alterations of stratified rocks by the contact of igneous rocks are common in the Caradoc, Stiperstones, &c. The trap rocks near Welshpool are in places columnar; the Breiddyn Hills are mostly greenstone, and yield elongated dykes in a north-east direction, which traverse the new redsandstone. Mineral veins (yielding lead-ore) are plentiful in Lower Silurian rocks, in the Shelve district, adjacent to Organic Contents.-Polypiaria, 9; Crinoidea rare; Pla- the trap rocks of Corndon, and the altered sandstones of the gimyona, 8; Mesomyona, 2; Brachiopoda, 19; Gastero-Stiperstones. In a plan of Mr. More's of Linley Hall, the poda, 7; Monothala macea?; Polythalamacea, 27; Crus- chief proprietor of this district, upwards of 24 are laid down tacea, 3; Annelida, 1; Fishes, 1; Doubtful, 2 (in all about in the district of Shelve alone, excluding the tracts around 79 species). the Bog and Penally: so that, comprehending the principal portion of the mining-ground, we may say that it contains upwards of 30 metalliferous veins which have been profitably worked.' (Murchison, Sil. Syst., p. 282.)

Aspect of the Country.-Toward the base of the steep escarpment of a hill, which may contain the whole Ludlow formation, as in the Wigmore Valley.

Localities.-Ludlow; Usk.

Wenlock Limestone.

Mineral Character.-Grey, bluish, or pinkish crystalline and subcrystalline limestone, arranged in strata of concre tionary aspect, separated by much argillaceous matter.

Structure. As above stated, concretionary in detail, but stratified on a large scale with considerable persistence of the parts. The concretionary structure most remarkable at top and bottom.

Aspect of the Country.--Usually a prominent or terracelike escarpment, where the beds dip moderately; rising to insulated hills, where contortions prevail, as near Ludlow, Wenlock, Malvern Hills.

Organic Contents.-Polypiaria, 53; Crinoidea, 14; Plagimyona?; Mesomyona, 1; Brachiopoda, 28; Gasteropoda, 8; Monothalamacea, 2; Polythalamacea, 9; Crustacea, 14; Annelida, 1; Doubtful, 2 (in all about 132 species). Localities.-Dudley; Wenlock; near Usk. Wenlock Shale.

Mineral Character.-Dull argillaceous shale,. with concretions of impure argillaceous limestone, much analogous to the argillaceous Ludlow rocks.

Structure.-Laminated, with spheroidal calcareous concretions, especially toward the base.

Aspect of the Country. Owing to the wasting of the middle beds, this shaly mass is often the line of a valley. Organic Contents.-Polypiaria, 18; Crinoidea rare; Plagimyona, 1; Mesomyona?; Brachiopoda, 33; Gasteropoda, 4; Monothalamacea?; Polythalamacea, 5; Crustacea, 2; Annelida?; Doubtful, 2 (in all about 65 species). There are marine plants in this deposit, and we have seen them of a vermilion colour.

Locality.-Wigmore Valley.

Caradoc Sandstone.

Mineral Character.-Sandstones of various colours, more or less micaceous, sometimes quartzose or conglomeritic, with thin courses of impure limestone, especially in the upper part. (Where altered by igneous action, this sandstone becomes a sort of quartz rock.)

Volcanic grits, composed of materials derived from igneous action, and subsequently arranged in water, are mentioned by M. Murchison rather frequently. In the Shelve district they are traversed by lead veins; in the Caradoc Hills, they abound, and were noticed as allied to greenstone' in the Wrekin by Mr. A. Aikin. They contain organic remains in several places, as near the Corndon Hills.

On reviewing the series of strata comprised in the Silurian System, in the vicinity of Ludlow, Usk, Llandeilo, or Denbighshire, we see them to form in reality one closely associated sequence of oceanic deposits-apparently accumulated with little local disturbance and very slight admixture of organic exuvia from the land. Volcanic eruptions appear to have rather varied than greatly disturbed this system of operations, though it is evident they contributed no small part of the granular materials of the principally sedimentary strata. The formation of limestone is local:where coral prevailed, we find the Aymestry and Wenlock limestones, and even the calcareous parts of the Landeilo rocks, to be in a great degree filled with coral. The Brachiopod shell Pentamerus' fills some whole beds of limestone (near Aymestry), and where it is deficient the limestone also fails, as in the district of Usk. In their course from Shropshire, northward to Denbighshire, Mr. Bowman (Reports of the British Association for 1840-41) has found the general type of the Silurian rocks to vary, and the line of distinction between it and the slaty strata below to be extremely obscure; and similar observations are recorded by M. Murchison in the account which he gives of these rocks in Caermarthenshire and Pembrokeshire.

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Mineral character alone will scarcely suffice, anywhere, for any but an arbitrary (and therefore unsatisfactory) boundary-line between the Silurian and Cambrian deposits. It is extremely probable, perhaps we may say it is already proved, that no distinction of higher value can be found on comparing the organic remains of these groups. In Snowdon (supposed to be very low in the Cambrian series of rocks) are shells and corals, which are perhaps the same, but cer tainly are congeneric with and very similar to Silurian ' fossils; and there is really as great (if not greater) difference between the Llandeilo and Wenlock rocks, in regard to Pla-fossils, than between the Silurian and Cambrian strata.

Structure. Usually laminated. Where altered by heat, the stratification is nearly or quite lost.

Aspect of the Country.-Very characteristic where the strata are indurated by vicinity of trap-rocks: the quartzose masses then assuming very picturesque forms. Organic Contents.-Polypiaria, 12; Crinoidea rare;

If we turn to other districts where Silurian fossils occur | Crinoidea, and Crustacea are most numerous in the princi plentifully (North America, Ireland, Norway), the result pal calcareous rock, Wenlock limestone; Brachiopoda are appears the same. There is apparently only one great series most plentiful in Caradoc sandstone; Cephalopoda, in the of organic combinations distinguishable among the fossili- Wenlock shale; fishes, in the upper Ludlow rock. ferous strata anterior to the old red-sandstone æra, and it Mr. Murchison gives the following general recapitulation was with a perception of this important truth that Mr. Mur- of organic remains in these strata chison once proposed for the Silurian strata the title of Protozoic. If instead of this we employ Palæozoic (as suggested by Sedgwick), and adopt the general view advocated in this work [PALEOZOIC; SALIFEROUS SYSTEM], we shall rank all the fossiliferous strata of the Cumbrian, Cambrian, and Silu rian groups as Lower Paleozoic Strata.

The lower arbitrary boundary of the Silurian strata being thus softened or erased, we may regard its upper surface as only locally more definite. Certainly in all the region around Wales the separation of the Silurian and old red deposits is somewhat sudden; the colour changes from grey to red; the dull mudstones become micaceous sandstones; the richly fossiliferous Upper Ludlow loses its character in unprolific red marls and grits. What few fossils do occur in these overlaid strata (except near the very bottom) are of quite other types of organization. But these are local truths, depending mainly on the introduction of new sediments poisonous to marine invertebral life; and as these sediments are very local, we may find in other countries groups of strata newer than the Silurian, older than the Carboniferous, with fossils intermediate in character and

combination to both.

This expectation is in course of fulfilment, but it is not yet fully satisfied. In Devonshire, the Rhine Valley, the Eifel, we find numerous assemblages of such Middle Paleozoic fossils, but they do not by any means fill the whole in terval between the Silurian and Carboniferous types; nor have we seen in collections from North America, Australia, the Hartz, Brittany, or Russia, all that is desired to fill the void. Ever alive to this most interesting inquiry, the author of the Silurian System' is perhaps at this moment adding valuable facts concerning it, the fruit of his continued researches in Russia; and we believe that by further examination of the lower strata of the Rhine Valley, and the Harz, some additional data may be gathered.

Pisces
Crustacea
Annelida

Mollusca (Heteropoda*)
(Cephalopoda)
(Gasteropoda)

Conchifera (Brachiopoda).

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Genera.

Species

15

24

10

37

5

6

11

6

41

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SILU'RIDÆ, a family of fishes of the order Malacopterygii, placed by Cuvier, in his Règne Animal,' between the Esocide, or Pike tribe, and the Salmonida, or family of the Salmons; but in the 'Histoire Naturelle des Poissons, the present group commences the Malacopterygii. The family Siluride constitutes a very extensive section of fishes, the species of which are for the most part confined to the fresh waters of warm climates. No group perhaps presents greater diversity of form than the Silurians, and their habits are equally interesting. Their most obvious external characters are, the want of true scales; the skin is generally naked, but in parts protected by large bony plates; the foremost ray of the dorsal and pectoral fins almost always consists of a strong bony ray, often serrated either in front or behind, or on both sides. These fishes moreover frequently are furnished with a small adipose fin on the hinder part of the back, as in the Salmonide. The mouth is almost always provided with barbules.

The genus Silurus, as now restricted, is distinguished by the dorsal fin being very small, without any distinct spine, and situated on the fore part of the back; the anal fin is of great length, extending along the whole belly of the fish, and sometimes joining the tail-fin; the maxillaries and intermaxillaries are furnished with small thick-set curved teeth, and there is a band of similar teeth on the vomer.

The species of this genus are confined to the old world; the only known European species is the Silurus glanis (Linn.), a fish of very large size, which is found in the lakes of Switzerland, in the Danube, the Elbe, and all the rivers of Hungary. In Prussia and Sweden it is also found.

The Silurus glanis is introduced in several works on the

been suspected that the so-called Silurus, supposed to have been found formerly in some of the Scottish rivers, might

have been the burbot.

At present the most important of the discoveries which (however incompletely) represent a Middle Paleozoic Period, have been in Devonshire and Cornwall, in the Fichtelgebirge, and in the Eifel and Rhine Valley. The principal of these, at least in regard to the analogies which it offers to the strata of earlier and more recent date, is the district of Devon and Cornwall; from which ten years ago only a small number of fossil species was known, but which has now yielded to numerous inquirers fully 300 distinct and recognisable forms. Of these, according to Mr. Lonsdale, he examined, and to Mr. Murchison and Professor Sedg-fishes of this country. It has however, says Mr. Yarrell, who gives (Geol. Trans. 1840) a table of the species which wick, who enumerate 128 species, a few of these species are found in the Silurian and a few in the Carboniferous rocks. Professor Phillips, in his recent work (Paleozoic Fossils of Devon and Cornwall), discusses the relations of 275 species, and arrives at the conclusion that both by numerical valuations of the general combinations of groups of invertebrata, and by specific analogies, the conclusion of the intermediate age of the Devon and Cornwall strata is confirmed. As the differences of the Devonian and Silurian fossils are very much greater than those between the Silurian and Cambrian fossils, it appears probable that the boundary assumed by Mr. Murchison for the upper termination of the Silurian Toup may remain with but slight alteration. One change contemplated by the author himself we should be glad to see adopted :-there are some fossiliferous bands placed by Mr. Murchison near the base of the old red system, which would better go to the Silurian ranks, since, in respect of the shells which they contain and their mineral composition, they are scarcely distinguishable from Silurian strata.

On considering the distribution of organic remains in the successive stages of the Silurian rocks, it is evident that the greatest variety of species occurs in the lower part of the upper and towards the upper part of the lower Silurian rocks. In other words, the conditions favourable to organic life in the sea were in the earliest period considerable; they arrived at a maximum in the middle part of the period, in the Caradoc sandstone, the Wenlock shale and the Wenlock limestone, and still continued considerable till the Silurian depositions ceased, and were replaced by old red-sandstone nearly devoid of organic remains. Polypiaria,

Cuvier states that this fish is sometimes upwards of six feet in length, and is said to weigh three hundred pounds (French). The body is elongated, and has the hinder part compressed, but towards the head its width gradually increases, and the head itself is depressed and large; its colour is dark-green above, of a pale-green below the laterai line, and yellowish on the belly, and the whole body is covered with dark spots; six barbules surround the meath, and two of these, which have their origin (one on each side) just above the angle of the mouth, are very long.

Mr. Yarrell observes, The Silurus is represented as sluggish in its habits, and a slow swimmer, taking its prey by lying in wait for it, in a manner somewhat similar to the Angler, Lophius; hiding itself in holes or soft mud, and apparently depending upon the accidental approach of fishes or other animals, of which its long and numerous barbules may be at the same time the source of attraction to the victims, and the means of warning to the devourer. From its formidable size, it can have but few enemies in the fresh water; and from them, its dark colour, in addition to its habit of secreting itself either in holes or soft mud, would be a sufficient security. In spring, the male and female may be seen together, about the middle of the day, near the banks or edges of the water, but scon return to their usual retreats. The ova, when deposited, are green; and the

These, in the preceding paragraphs, we have called Monothalamacea.

young are excluded between the sixteenth and nineteenth | chiostegous rays are twelve in number; the teeth are longer days.

The flesh of the Silurus is white, fat, and agreeable to many persons as food, particularly the part of the fish near the tail; but on account of its being luscious, soft, and difficult to digest, it is not recommended to those who have weak stomachs. In the northern countries of Europe the flesh is preserved by drying, and the fat is used as lard.'

It appears by some statements in the 'Histoire Naturelle des Poissons,' that the present fish is so voracious, that it has been known, in several instances, to devour children; and in one instance the body of a woman was found in one of these fishes.

Several examples of the restricted genus Silurus are found in Asia.

Cuvier separates from the typical Siluri, as a genus, the Silurus mystus of Linnæus, and some others, on account of the compressed form of the body, and the dorsal fin having a strong bony spine in front, which is denticulated on the hinder margin. The body is deepest near the middle, but tapers somewhat suddenly towards the extremities. The head is small and depressed, and the eyes are placed low down.

The species upon which Cuvier founds this genus-to which he applies the name Schilbe-are found in the Nile, but there are others described in this author's great work on fishes, one of which is found at Senegal and another in India.

Genus Cetopsis.-This genus is founded by Agassiz on certain species found in Brazil, which in their affinities approach the genus Silurus, but are distinguished by the extremely small size of their eyes.*

Genus Bagrus, Cuvier. The species of this genus are distinguished from those of the genus Silurus, as restricted, by their possessing an adipose fin on the hinder part of the back. The body is naked-that is, unprovided with bony plates-and the mouth is provided with barbules, the number of which, varying in different species, has been selected for the minor divisions of the group. Numerous species are found in the Indian and African rivers.

Genus Pimelodus, Lacép.-Differs from Bagrus in having no teeth on the vomer; the palatines however are often provided with teeth. The species vary much in the number of their barbules, and in the form of the head, which is often protected by a bony plate, and a large bony plate is situated between that on the head and the dorsal spine; similar bony plates on the head however are observable in many of the species of the preceding genus. The species of Pimelodus are very numerous, and are found both in the Old and New World. Numerous species are described from North America, others are found in South America, and the rivers of India also furnish numerous examples.

Genus Phractocephalus, Agassiz.-This genus contains but one species, an inhabitant of the Brazils; its generic distinction consists in its possessing some incomplete osseous rays enchased in the upper margin of the adipose fin. The head is depressed and covered by a deeply sculptured bony plate; a second bony plate, of a transverse oval form, is situated in front of the first dorsal fin. The branchiostegous rays are nine in number, and the mouth is provided with six barbules.

Genus Platystoma, Agassiz, is composed of several South American species of Siluridae which have the muzzle depressed, and are remarkable for the great number of their branchiostegous rays, which amount in some to fifteen in number. Some of the species attain a large size, there being specimens in the Paris Museum as much as five feet in length, and they have been seen of still greater bulk. Genus Galeichthys, Cuv. and Val.-This genus is nearly allied to Bagrus, but distinguished by the head being round and unprotected by any distinct bony plate: the branchiostegous rays are six in number. Some possess six barbules, and others have four. One species is found at the Cape of Good Hope, a second is said to be found both in North America and at Rio Janeiro; several species occur in Brazil, and the Ganges also furnishes a species of the present genus.

Genus Silundia, Cuv. and Val.-This genus is founded upon a fish from the Ganges, which has the head small and smooth, a very small adipose fin, and a long anal fin. It has but two barbules, and they are very small; the branSee the part on Iehthyology of the 'Voyage of MM, Spix and Mar

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and less abundant than usual in the Silurida. The only species known (Silundia Gangetica, Cuv. and Val.; Pimelodus Silundia of Hamilton) is said to be very common at the mouth of the Ganges, and to be much esteemed for food.

Genus Arius, Cuv. and Val.-Contains many species of Silurida, allied to the Bagri, but distinguished by their palatine teeth forming two distinct and widely separated masses. In some species the teeth are minute and dense, like the pile on velvet, or like the teeth of a carding-machine, and in others the palate is furnished with teeth in the rounded form of paving-stones, instead of having them pointed. Species of this genus are found in the tropical portions of both continents, and also in North America. Genus Auchenipterus, Cuv. and Val.-May be distinguished from other genera which possess the adipose fin by the small size of the head, the very minute size of the teeth, and there being five branchiostegous rays. It evinces an affinity with Pimelodus in having no palatine teeth, and in the number and form of the maxillary barbules. The first dorsal is situated very forward, a circumstance which suggested the generic name. The bony shield which covers the upper surface of the head is, in the fishes of this genus, united by a suture with the dilated bony nuchal plates. All the known species are from the tropical portions of South America.

Genus Trachelyopterus.-The genus is founded by MM. Cuvier and Valenciennes, upon a small Silurian from Cayenne, in which there is no adipose fin; the teeth are fine, like the pile of velvet, and the palate is destitute of teeth; the barbules are six in number. The head is somewhat short, and protected by a stout bony shield, which is united almost immediately with the dorsal on account of the shortness of the interparietal plate, and almost rudimentary state of the chevron, placed generally in front of the spiny rays of the dorsal fin; the pectoral fins are inserted as it were under the throat.

Genus Hypophthalmus (Spix), Cuv. and Val.-This genus is composed of but few species, and these are from the tropi cal portions of South America. The principal characters are:-Mouth destitute of teeth; eyes placed very low down near the angle of the mouth; branchiostegous rays fourteen in number; body furnished with an adipose fin.

Genus Ageneiosus (Lacépède), Cuv. and Val.-This genus is thus characterised in the Règne Animal:'-Characters the same as in Pimelodus, excepting that there are no barbules properly so called. In some, the maxillary bone, instead of being prolonged into a fleshy and flexible barbule, assumes the form of a projecting denticulated horn. In others this bone does not project, but is concealed under the skin; the dorsal and pectoral spines are but little apparent. All the species are from South America.

Genus Synodontis, Cuv.-This genus is composed of Silurians found in the Nile and Senegal, which have an adipose fin, the muzzle narrow, and terminated by an ethmoid which supports two small intermaxillary bones armed with bristle-like teeth; the lower jaw composed of two short and slender rami, bearing in front a mass of teeth which are in the form of very slender lamina and closely packed-each of these teeth is attached to the jaw by a flexible and very slender stalk. The stout bony plate which covers the head is joined to the nuchal plate, and this extends to the first spine of the dorsal fin, which is of very large size, and in this respect resembles the first spine of the pectoral fins. The inferior barbules, and sometimes the maxillary barbules, have small lateral branches.

Genus Doras, Lacépède.- The species of this genus are distinguished by the lateral line being armed with bony plates, which are carinated, and terminate in a spine. They have a second adipose dorsal fin, and the foremost spine of the pectoral and anterior dorsal fins is very large and deeply serrated. Osseous plates cover the upper surface of the head and extend to the dorsal fin, and the humoral bone is produced backwards and pointed.

These may be regarded, say the authors of the 'Histoire Naturelle des Poissons,' as the most powerfully armed of all the Siluride; thus the Spanish colonists in South America have given to them the name Mata-caïman (or Crocodile-killer), because it often happens that when they are swallowed by these large reptiles, the esophagus and pharynx of those animals are so lacerated by the spines of the Silurus as to cause death. Strabo also (p. 824, Casaub.

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