[425]This specimen is now in the British Museum.
[425]This specimen is now in the British Museum.
Lign. 164. Turrilites tuberculatus, (Bosc.)nat.Chalk-marl, Lewes.Showing the form of the aperture, and the spinous tubercles. The specimen is a cast in indurated chalk-marl; the last wreath only is figured.Fig.1.—Posterior view, exhibiting the expanded outer lip, and the obtuse termination of the columella.2.—Front view, showing the form of the aperture.a.—Two tubercles, bearing spines.
Lign. 164. Turrilites tuberculatus, (Bosc.)nat.
Lign. 164. Turrilites tuberculatus, (Bosc.)nat.
Chalk-marl, Lewes.
Showing the form of the aperture, and the spinous tubercles. The specimen is a cast in indurated chalk-marl; the last wreath only is figured.
The Chalk-marl of Lewes, of the Sussex coast, and of the cliffs near Dover, and the Upper Green Sand of Dorsetshire, have yielded the principal British specimens of this genus. Several species occur in the lower cretaceous strata, at St. Catherine’s Mount, near Rouen, associated, as in England, with Scaphites, Hamites, and other allied genera.[426]
[426]See Fossils of the South. Downs for figures of many species of the Cephalopoda of the Sussex Chalk.
[426]See Fossils of the South. Downs for figures of many species of the Cephalopoda of the Sussex Chalk.
APTYCHUS.
Lign. 165. Aptychus sublævis.1/2nat.Kimmeridge Clay, Hartwell, Bucks.Fig.1.—The convex surface.1a.—Magnified section of portion.2.—The concave side.
Lign. 165. Aptychus sublævis.1/2nat.Kimmeridge Clay, Hartwell, Bucks.
Aptychus, Meyer. (Trigonellites,Parkinson.)Lign.165.—Associated with the remains of Ammonites in several localities, are found flattened triangular bodies, from less than an inch to an inch and a half in diameter, the nature of whichis still somewhat problematical. A good figure is given by Mr. Parkinson of one species (Org. Rem.vol. iii. pl. xiii. figs. 9, 10, 12. SeePict. Atlas), with the nameTrigonellites latus. These bodies frequently occur in pairs and in apposition, as in the specimen figured inLign.165. Their structure is cellular; one surface is slightly concave and striated, and the other covered with minute circular pores. Altogether their appearance is that of bodies enclosed in vascular integuments. It is supposed that they are the opercula of Ammonites. These fossils are commonly found in the last or body chamber of Ammonites, in the Oxford Clay, near Chippenham, the Coral Oolite of Malton, the Lias of Lyme Regis, and the lithographic limestone of Solenhofen. M. Ewald states that they may be found in the ChalkScaphitesby making a longitudinal section of the body chamber: but I have not succeeded in detecting them in the examples from the chalk-marl which I have broken up for that purpose. As these bodies (alluded to by authors asTrigonellites,Aptychus,Munsteria, &c.) will probably come under the observation of the collector, especially among the fossils of the Kimmeridge Clay, these remarks are introduced to suggest diligent research, in the hope that the origin of these fossils may at length be discovered.
DISTRIBUTION OF FOSSIL CEPHALOPODA.
Geological Distribution of Fossil Cephalopoda.—Even from this short review of the principal types of the fossil Cephalopoda, the great interest which attaches to thestudy of this class of organic remains is strikingly demonstrated. Their geological distribution is alike replete with phenomena of an important character. In the Lower Palæozoic (Lower and Upper Silurian) strata, the chambered mollusks belong (with a very few doubtful exceptions) to the Nautilidæ, namely, Nautilus, Lituites, Cyrtoceras, Orthoceras, &c. The Devonian and Carboniferous systems contain Nautilus, Clymenia, Gyroceras, Cyrtoceras, and Orthoceras, together with a peculiar group of Ammonitidæ, theGoniatites. The Trias in general is extremely poor in Cephalopoda; the Permian group affording but two species of Nautilus, and the Muschelkalk two other species: but, in addition to these, the Muschelkalk contains Ceratites, which is a genus peculiar to the Triassic group, and chiefly abounds in the St. Cassian beds (in the Austrian Alps), where it is accompanied by Nautilus, Orthoceras, Ammonites, and Goniatites. In the Lias and Oolite Nautili abound, and we meet for the first time with Belemnites. The same families, viz. Nautilidæ, Ammonitidæ, and Belemnitidæ, prevail throughout the Cretaceous strata. The Tertiary formations contain a few Nautilidæ only; no vestiges of the Ammonitidæ and true Belemnitidæ, which, as we have seen, swarmed in the ancient seas, are perceptible, while in the existing oceans, theNautilusandSpirulaare the sole representatives of the numerous shell-bearing cephalopoda of the ancient geological eras. Thus, the Nautilidæ extend from the oldest to the newest fossiliferous strata, the genus being still in existence: the Ammonitidæ, on the other hand, though less ancient in origin, do not pass beyond the limits of the cretaceous epoch.
In the following tabular arrangement these facts are placed in a more distinct point of view:—
Tabular View of the Distribution of Cephalopoda through the Geological Epochs.
[427]The Ammonitidæ are from the St. Cassian beds only.
[427]The Ammonitidæ are from the St. Cassian beds only.
With regard to the zoological affinities between the living and extinct species of testaceous Cephalopoda, Dr. Buckland remarks, "that they are all connected by one plan of organization; each forming a link in the common chain which unites the existing species with those that prevailed among the earliest conditions of life upon our globe; and all attesting the identity of the design that has effected so many similar ends, through such a variety of instruments, the principle of whose construction is, in every species, fundamentally the same.
"Throughout the various living and extinct genera of these beings, the use of the air-chambers and siphuncle of their shells, to adjust the specific gravity of the animals in rising and sinking, appears to have been identical. The addition of a new transverse plate within the coiled shell added a new air-chamber, larger than the preceding one, to counterbalance the increase of weight that attended the growth of the shell and body of these animals." (Bd.p. 380.)
The occurrence of the Nautilus, and its congeners, among the earliest traces of the animal kingdom, and their continuance throughout the immense periods during which the family of Ammonitidæ was created, flourished, and became extinct, and the existence of species of the same genus at the present time, are facts too remarkable to have escaped the notice even of those who are not professed cultivators of geological science; and I am induced to quote the following beautiful lines, by Mrs. Howitt, to impress this interesting phenomenon more strongly on the mind of the youthful reader.[428]
[428]The poetess has, however, not been literally accurate regarding the Nautilus and its habits, nor as to the formation of stratified rocks, but has given a romantic rather than a scientifically correct view of this interesting Cephalopod, and of the disappearance of its congener. The young reader must, therefore, remember that the Nautilus sometimesfloats, butnever sails; and that the whole race of Ammonitesdied outin course of time, and were not annihilated by convulsive movements of earth and sea.
[428]The poetess has, however, not been literally accurate regarding the Nautilus and its habits, nor as to the formation of stratified rocks, but has given a romantic rather than a scientifically correct view of this interesting Cephalopod, and of the disappearance of its congener. The young reader must, therefore, remember that the Nautilus sometimesfloats, butnever sails; and that the whole race of Ammonitesdied outin course of time, and were not annihilated by convulsive movements of earth and sea.
"TO THE NAUTILUS.
"Thou didst laugh at sun and breeze,In the new created seas;Thou wast with the reptile broodsIn the old sea solitudes,Sailing in the new-made light,With the curl’d-up Ammonite.Thou surviv’dst the awful shock,Which turn’d the ocean bed to rock,And changed its myriad living swarms,To the marble’s veined forms."Thou wast there, thy little boat,Airy voyager! kept afloat,O’er the waters wild and dismal,O’er the yawning gulfs abysmal;Amid wreck and overturning,Rock-imbedding, heaving, burning,Mid the tumult and the stir;Thou, most ancient mariner,In that pearly boat of thine,Sail’dst upon the troubled brine."
"Thou didst laugh at sun and breeze,In the new created seas;Thou wast with the reptile broodsIn the old sea solitudes,Sailing in the new-made light,With the curl’d-up Ammonite.Thou surviv’dst the awful shock,Which turn’d the ocean bed to rock,And changed its myriad living swarms,To the marble’s veined forms.
"Thou wast there, thy little boat,Airy voyager! kept afloat,O’er the waters wild and dismal,O’er the yawning gulfs abysmal;Amid wreck and overturning,Rock-imbedding, heaving, burning,Mid the tumult and the stir;Thou, most ancient mariner,In that pearly boat of thine,Sail’dst upon the troubled brine."
ON COLLECTING FOSSIL CEPHALOPODA.
On the Collection of British Fossil Cephalopoda.—In the Tertiary formations of England, the remains of but seven species of Nautilus (comprising Aturia) have been noticed; the large species (N. imperialis) is the most common. These are generally in a good state of preservation, and only require the careful removal of the surrounding clay or marl. When pyrites largely enters into the composition of the specimens, the investing matrix can seldom be effectually cleared off: if the outer surface, and general form, be not well displayed, breaking the specimen will oftenexpose the inner cells, with the siphunculus, in a beautiful state. TheNautilus imperialisis occasionally imbedded in the septaria of the Isle of Sheppey, and of Bognor and Bracklesham, on the Sussex coast. Sections of such examples, in the vertical direction of the enclosed shell, afford, when polished, very brilliant and interesting fossils; the septa and the shelly tube of the siphunculus are often preserved.
The Cephalopods of the Cretaceous formation, with the exception of those in the argillaceous strata of the Galt, are generally destitute of their shells, and only occur in the state of casts; and the Chalk Nautili are liable to separate at the divisions of the septa, and an entire series of the casts of the chambers may sometimes be obtained, so as to display the entire form of the original shell. The Ammonites of the White Chalk, although mere casts, yet retain their configuration, the foliated margins of the septa dove-tailing them together. I have already mentioned that search should be made along the back of these specimens for the siphuncle, the shelly tube of which is sometimes well defined. In the Chalk-marl the casts are sharper than in the White Chalk, and generally of a deep ochreous colour, with the lines of the sinuous septa clearly defined. The siphuncle is occasionally preserved in pyrites, in the Ammonites, Nautili, Turrilites, and Scaphites; and the outer lip or margin of the mouth, or aperture, of the latter, and of the Ammonites, is frequently replaced by the same mineral.
The Ammonites, Hamites, &c. of the Galt have their pearly coat remaining, but this investment is extremely delicate; and although when first removed from the marl it is beautifully iridescent, the vivid hues are very evanescent, and the shell becomes opaque and of a light fawn colour. Very commonly the shell flakes off, wholly or in part, leaving a cast of indurated pyritous marl. I have preserved specimens with the shell many years, by applyinga thin coat of mastic varnish with a soft camel-hair pencil, before the marl had become dry, and while the shells were entire. The Galt Ammonites, like the Nautili of the London Clay, are often invested with pyrites, and have the inner cells and siphuncle well preserved.
The argillaceous strata of the Oolite and Lias contain Ammonites, &c. in much the same state of mineralization as those of the Galt. The Kimmeridge Clay, in some localities, particularly around Aylesbury (and especially at Hartwell Park, the seat of Dr. Lee), abounds in Ammonites with the shell as perfect and beautiful as if just dredged up from the sea. But, like the fossils of the Galt, few of the specimens are durable; although in many examples the shell may be preserved by the application of mastic varnish. The most common Ammonite at Hartwell isA. biplex(Sow. Min. Conch.), which varies from three inches to one foot in diameter; the surface is covered by very strong ribs that encircle the whorls. The shell is thick, and composed of several laminæ.[429]
[429]According to the observations of my son, the outer layers, when highly magnified, present an appearance of opaque areolæ, with irregular radiating fibres; the inner laminæ are covered with minute pores, apparently the orifices of tubuli, some of which are arranged singly in crescents, and others are confluent, like short strands of beads. I mention the fact to direct attention to the microscopic examination of the structure of these splendid fossils.
[429]According to the observations of my son, the outer layers, when highly magnified, present an appearance of opaque areolæ, with irregular radiating fibres; the inner laminæ are covered with minute pores, apparently the orifices of tubuli, some of which are arranged singly in crescents, and others are confluent, like short strands of beads. I mention the fact to direct attention to the microscopic examination of the structure of these splendid fossils.
The sparry casts of the separate cells of Ammonites which occur in some of the calcareous beds of the Oolite, will not fail to be observed by the collector. It is convenient to preserve such specimens either on a tray or board, in which a groove is made for their reception, or in a mould of gutta percha.
In collectingBelemnitidæ, the caution already given, of examining the surrounding clay or marl, must not be disregarded; the student should remember, that traces of the soft parts of the animals, even of mere impressions of the body andhead, with the tentacula and their acetabula, or little horny rings and hooks, are more important than the most splendid examples of the spathose durable osselet. The guards should be selected with especial reference to their containing the phragmocone (seeLign.141,fig.2), or chambered conical shell, in the alveolus or cavity of the upper and larger end. An apparently worthless fragment of a Belemnite will often be found to possess this part of the structure, as in the example figured, which, until fractured longitudinally, had been thrown by among useless duplicates. The search for the remains of the fossil naked Cephalopoda, as the Teuthidæ and Sepiadæ, and their ink-bags, must be made in a like cautious manner. In the Lias marls, the ink-bag and its duct is often found partially covered by a pellicle of nacre, without any trace of the other parts of the animal. A reference to Dr. Buckland’s plates (Bd.pl. xxviii. xxix) will familiarize the student with the appearance of these fossil remains.
LOCALITIES OF FOSSIL CEPHALOPODA.
A FEW BRITISH LOCALITIES OF FOSSIL CEPHALOPODA.
Abingdon, Berks. Ammonites, fine casts in spar and limestone; Middle Oolite.
Aylesbury, Bucks. Ammonites, several species; splendid examples ofA. biplex, with the shell remaining, in the Kimmeridge Clay.
Aymestry. Upper Silurian; Gomphoceras, Orthoceras, &c.
Bath. Fine Ammonites in the Oolite.
Beachy Head. Along the shore, gigantic Ammonites in the Chalk, at low-water.
Benson, Oxfordshire. Fine Hamites, in Chalk-marl.
Blackdown, Devonshire. Beautiful siliceous casts of Ammonites; Green Sand.
Bognor, Sussex. Nautili, in the Tertiary Clays and sandy Limestones; also, along the neighbouring coast, in Septaria.
Bolland, Yorkshire. Mountain Limestone; Goniatites.
Boreham, near Warminster, Wilts. Nautili and Ammonites in Green Sand.
Bracklesham Bay, Sussex. Nautili in Tertiary Clay.
Bridport, Dorset. Ammonites; Inferior Oolite.
Brighton. In the Chalk, Ammonites, Belemnitellæ, &c.
Brill, Lucks. Ammonites, as at Aylesbury.
Buxton, Derbyshire. Goniatites; Mountain Limestone.
Charmouth, Dorsetshire. Ammonites, Belemnites, &c.; Lias.
Cheltenham. Ammonites, Belemnites, Nautili, &c. in abundance; Inferior Oolite and Lias.
Chicksgrove, Tisbury, Wilts. Ammonites, several species; some chalcedonic; Upper Oolite.
Christian Malford, near Chippenham. In Oxford Clay, Belemnites, Belemnoteuthis, and Geoteuthis;very fine.
Clayton, near Hurstpierpoint, Sussex. In Chalk-marl, Ammonites, Nautili, and Turrilites; very fine specimens.
Closeburn, Dumfriesshire. Orthocerata, large species; Silurian.
Comb Down, near Bath. Ammonites and Nautili; Oolite.
Connaught, Ireland. Goniatites; Mountain Limestone.
Cork. Orthocerata; Mountain Limestone.
Crockerton, near Warminster. Ammonites, in Galt.
Dover. In the cliffs, and along the shore, in Chalk and Chalk-marl, Turrilites, Ammonites, Nautili, &c.
Dowlands, near Lyme. Fine Ammonites, &c. in the Lias.
Dundry, near Bristol. Ammonites, &c. Inferior Oolite.
Earlstoke, Wilts. Hamites, Ammonites, &c. in Green Sand.
Faringdon, Berks. In the gravel-pits, Nautili, Ammonites, &c. In the Coral Rag, beautiful casts in limestone and spar of Ammonites, Belemnites, &c.
Folkstone, Kent. In the Galt, at Eastware Bay, in the cliff, and along the shore at low-water, Belemnites, Hamites, Ammonites, &c. in profusion.
Hamsey, near Lewes, Sussex. Chalk-marl; Turrilites, Scaphites, Hamites, Baculites, Crioceratites, Ammonites, Nautili; Belemnites, very rare.
Hartwell, Bucks, seat of Dr. Lee. Splendid Ammonites, with their shells, in Kimmeridge Clay.
Heytesbury, Wilts. Nautilus elegans, and other Chalk-marl Cephalopoda.
Horncastle. Very fine Ammonites.
Hythe, Kent. In Green Sand, large Ancyloceratites, Ammonites, &c.
Ilminster, Somerset. Upper Lias, Ammonites; Marlstone, Belemnites and Ammonites.
Kelloway. Many beautiful Ammonites, &c.; Middle Oolite.
Keynsham, near Bristol. Splendid Nautili and Ammonites; the largeA. giganteus, two or three feet in diameter; and specimens with the chamber filled with spar, of surpassing beauty; Lias.
Lewes, Sussex. Nautili, Ammonites, &c. in the Chalk and Marl quarries of the vicinity.
London. Tertiary strata in the vicinity. Highgate Hill, fine Nautili, and Aturia ziczac, Beloptera, &c.
Ludlow. Upper Silurian; Lituites, Orthoceras, Phragmoceras, &c.
Lyme Regis, Dorsetshire. Ammonites, Nautili, Belemnites, Sepiæ, &c. in profusion in the Lias; and Scaphites and Turrilites in the Chalk.
Lympne, Kent. Ammonites, Ancyloceratites, &c. in Green Sand.
Maidstone, Kent. Ammonites, of large size, in Shanklin Sand.
Malton. Ammonites, several large species. Lower Oolite.
Marsham, near Abingdon. Ammonites; Oolite.
Marston Magna, near Ilchester.Ammonite-marble; Lias.
Newton Bushel, Devonshire. Nautilus, Orthoceras, Cyrtoceras, Goniatites, &c. in the Devonian rocks.
Norwich. In Chalk, Belemnites in profusion; Ammonites, &c.
Nutfield, Surrey. Fuller’s-earth pits: beautiful Nautili (N. undulatus, andA. Nutfieldiensis), and Ammonites.
Offham, near Lewes. In the Chalk-pits, large Ammonites; Chalk-marl in a pit, on the right-hand side of the road, a quarter of a mile north of the village, Hamites, Turrilites, Scaphites, Nautili, rare species of Ammonites, &c.
Oxford. Quarries in the vicinity, Ammonites, Belemnites, &c.
Petherwin, Cornwall. Clymenia, Goniatites, Orthoceras, &c. in the Upper Devonian rocks.
Portland. Upper Oolite; gigantic Ammonites.
Roak, near Benson, Oxfordshire. In Chalk-marl, Hamites, Ammonites, &c.
Scarborough. Kelloway Rock; Ammonites, &c.
Scarlet, Isle of Man. Nautili, &c.; Mountain Limestone.
Settle, Yorkshire. Goniatites; Mountain Limestone.
Sherbourn, Somersetshire.Ammonite-marble; Lias.
Southerham, near Lewes. In the Chalk-pits, large Ammonites; in the Marl, Nautili, Ammonites, Turrilites, &c.
South Petherton, Somerset. Marlstone; Belemnites and Ammonites in profusion.
Speeton, Yorkshire. Galt; Crioceras, Ancyloceras, &c.
Steyning, Sussex. In Chalk-marl near the town, Belemnites (B. lanceolatus), Nautili, Ammonites, &c.
Swindon, Wilts. In the Portland-stone quarries, Ammonites, in abundance; principally casts ofA. biplex, andA. triplicate. In the Kimmeridge Clay in the vicinity, Ammonites with the shell preserved.
Tisbury, Wilts. In Portland-stone, fine Ammonites, often chalcedonic (seeBd.pl. xli.).
Trowbridge, Wilts. In Oxford Clay, Ammonites, Belemnites, &c. were obtained in great numbers during the railway cuttings.
Watchett, Somersetshire. Ink-bags of Sepiadæ, &c.; splendid Ammonites; Lias.
Whitby, Yorkshire. Ammonites, Belemnites, &c. in abundance; Nautili, &c.; Lias.
Yeovil, Somersetshire. Nautili and Ammonites; Inferior Oolite.
FOSSIL ARTICULATA; COMPRISING THE ANNELIDES, CIRRIPEDES, CRUSTACEANS, AND INSECTS.
Thedivision of the Animal Kingdom termedArticulata, embraces, as the name implies, those animals which have ajointedbody, generally possessing an external-jointed skeleton, composed of segments more or less annular and distinct. It comprehends six classes; namely—
Of the first, third, fourth, and sixth of these classes, remains occur in the British strata, some being referable to existing, but the greater part to extinct species and genera. I propose to describe a few illustrative examples of the fossils belonging to each Class.
Annelida.—This name is given to a class ofArticulata, consisting of worms, whose bodies are formed of little rings, or annular segments, and which have red blood; as the Leech, Earth-worm, &c. Some are naked (theDorsibranchiataandAbranchiata), and move with great celerity; as theGordius, or Hair-worm, and theNereis, so frequent on the sands of the sea-shore. Others have shelly coverings(theTubicolæ), as theSerpula, and are sedentary, or fixed to other bodies. The soft bodies of certain species are protected by a coat, or tube, formed by the agglutination of sand, or other foreign substances, as in theSabella(Lign.123,fig.6, p. 385).
The fossil remains of the testaceous Annelides are very abundant in some deposits; and even the naked, flexible, soft-bodied forms have left proofs of their existence in some of the most ancient sedimentary rocks. Traces of nine species, belonging to five genera of these soft, naked Annelides, have been observed in the Silurian strata of Britain.
Lign. 166. Fossil impression of Nereis.Silurian strata.(Drawn by Miss Murray.)Nereites Cambrensis.(Murch. Sil. Syst.)Llampeter.
Lign. 166. Fossil impression of Nereis.Silurian strata.(Drawn by Miss Murray.)Nereites Cambrensis.(Murch. Sil. Syst.)Llampeter.
FOSSIL NEREIS. SERPULA. CIRRIPEDIA.
The first notice of these remarkable remains appeared in the invaluable work of Sir R. I. Murchison on the Silurian System.[430]The living species ofNereis(Dorsibranchiate) arefree, agile animals, having a distinct head, provided with either eyes or antennæ, or both; they are the most perfect in structure of all the Annelides. The fossil represented inLign.166indicates that the body of the original was composed of about one hundred and twenty segments; the feet were half the length of a segment of the body; and thecirriof the feet were longer than such segment. A more slender species, (Nereites Sedgwickii,) the body consisting of a greater number of segments, is also figured and described by Sir It. I. Murchison. Other impressions in the same stone resemble those that would be produced by smooth Annelides (Abranchiate) related to theGordius, or Hair-worm.[431]
[430]Murch. Sil. Syst. p. 699.[431]Murch. Sil. Syst. p. 701, pl. xxvii.; and M’Coy, Cambridge Pal. Foss. p. 128, pl. 1. D.
[430]Murch. Sil. Syst. p. 699.
[431]Murch. Sil. Syst. p. 701, pl. xxvii.; and M’Coy, Cambridge Pal. Foss. p. 128, pl. 1. D.
Serpula.—The animals of this genus are sedentary or fixed, having calcareous tubes or shells, but to which they have no muscular attachment. They have plumose or arborescent gills affixed to the anterior part of the body. The shelly tubes of theSerpulæare constantly seen on our coasts, encrusting stones, rocks, shells, sea-weeds, &c., and may be known by their contorted or twisted forms. There are a hundred and fifty British fossil Tubicolæ. A large species has been discovered in the Silurian rocks (Murch. Sil. Syst.pl. v.fig.1); several occur in the Carboniferous, Oolitic, and Cretaceous, and many in the Tertiary strata. In the Upper Chalk, a smooth tortuousSerpulais not uncommon (S. plexus,Min. Conch, tab. 598); it occurs in masses several inches long. But I have not observed either in the Chalk, or in any other deposit, indications of banks ofSerpulidæ, like those now in progress off the Bermudas, and which resemble coral-reefs in their solidity and extent.
Cirripedia.—These animals have a soft body, enveloped in a membrane, which in some genera is protected only by a horny sheath, but in general is enclosed in a shell composedof various calcareous plates.[432]They have six pairs of feet, terminating in long, slender, articulated tentacula, furnished with cilia, and coiled up like tendrils at the extremities near the mouth. The name of the class (curled-feet) has originated from the appearance presented by the curled tentacula when projecting from the oval aperture of the shell. The testaceous Cirripedes orBarnaclesare divided into two groups; namely, thesessile, or those which in their adult state are fixed by the base to other bodies, (Balanidæ,) as the Acorn-shell, orBalanus; and thepedunculated, which have a process of attachment, peduncle or stem, (Lepadidæ,) as the Duck-barnacle, orLepas. But the young animals of these genera have powerful locomotive organs, and are capable of swimming, by sudden jerks, like some of the crustaceans, to which class, especially in this stage of their existence, they closely approach. But after a short period of freedom, the young Cirripede fixes itself in some locality suitable to its economy, and rapidly undergoes the transformation which results in the sessile adult Barnacle or Lepas.[433]
[432]Until within the last few years the valves of theCirripedeshave been generally figured and described in works on Conchology as being allied to theMollusca.[433]See Mr. C. Darwin’s admirable Monograph on the Cirripedia, published by the Ray Society, 1851.
[432]Until within the last few years the valves of theCirripedeshave been generally figured and described in works on Conchology as being allied to theMollusca.
[433]See Mr. C. Darwin’s admirable Monograph on the Cirripedia, published by the Ray Society, 1851.
Balanus.Lign. 167, fig. 1.—The shell of this sessile Cirripede is of a conical shape and cellular structure. It consists of a thick plate at the base, or place of attachment; of a series of plates, united by sutures, arranged around the body of the animal, and calledparietalvalves; and of pieces termedopercularvalves, by which the aperture is closed. The shell of theBalanus, so common on the rocks of our shores, and on every pile and pier within reach of the tide, is composed of six parietal, and four opercular valves. ThefossilBalanus,Lign.167.fig.1, is from theCrag, a formation containing many shells of this genus: in this example, the six parietal plates of the conical shell only remain, but in some specimens the opercular valves are also preserved. There are about twelve species of Balanus in the Crag; but none have been found either in the older Tertiary, or in the secondary rocks of England. In the newerPliocenedeposits of the Sub-Apennines, and of North America, several species are common.
Lign. 167. Fossil Barnacles and Pholades.Fig.1.—Balanus tesselatus.(Sow. Min. Conch.)Crag.Suffolk.2.—Loricula pulchella.(Mr. G. B. Sowerby, jun.)Chalk.Kent.a.The situation of the aperture of the shell.3.—A valve (Tergum) ofScalpellum maximum.Chalk.Lewes.4.—Another valve (Carina) of the same species.5.—Pholas priscus[434]; in wood.Lower Green Sand.Sandgate.a.One of the shells seen in profile.6.—Univalve Shells (Neritæ) in hollows formed byPholades.(Mr. Bensted.)Lower Green Sand.Maidstone.a.TheNeriteslodged in the cavities.b.Fragment of wood remaining attached.
Lign. 167. Fossil Barnacles and Pholades.Fig.1.—Balanus tesselatus.(Sow. Min. Conch.)Crag.Suffolk.2.—Loricula pulchella.(Mr. G. B. Sowerby, jun.)Chalk.Kent.a.The situation of the aperture of the shell.3.—A valve (Tergum) ofScalpellum maximum.Chalk.Lewes.4.—Another valve (Carina) of the same species.5.—Pholas priscus[434]; in wood.Lower Green Sand.Sandgate.a.One of the shells seen in profile.6.—Univalve Shells (Neritæ) in hollows formed byPholades.(Mr. Bensted.)Lower Green Sand.Maidstone.a.TheNeriteslodged in the cavities.b.Fragment of wood remaining attached.
[434]Figs. 5 and 6 are referred to and described at pages409and410, vol. i.
[434]Figs. 5 and 6 are referred to and described at pages409and410, vol. i.
Lepadidæ.—The pedunculated Cirripedes, of which the commonDuck-barnacleis a well-known example, have a strong, muscular, hollow stalk, or peduncle, which supports a multivalve shell, containing the body of the animal. InPollicipesandScalpellumthere are small calcareous plates covering the junction of the body with the peduncle. Detached valves of several species of these two genera are met with in the Chalk, Galt, and Shanklin Sand, of Kent and Sussex; and three species have been found in the English Tertiary beds.[435]The valves of these fossil Cirripedes are most usually found in a disconnected state (Lign.167,figs.3 and 4); but the TertiaryScalpellum quadratumis sometimes better preserved; and Mr. Morris has described a most beautiful group ofPollicipes(P. concinnus), attached to an Ammonite, from the Oxford Clay. Mr Wetherell, of Highgate, has also discovered, in the Upper Chalk, near Rochester, an almost perfect Cirripede, named by Mr. G. B. Sowerby, jun.,Loricula pulchella(Lign.167,fig.2), and lately more fully described in detail by Mr. Darwin.[436]
[435]See Mr. Darwin’s Monograph of the FossilLepadidæ, Palæontographical Society, 1851.[436]Monograph of the Fossil Lepadidæ, p. 81, pl. v.
[435]See Mr. Darwin’s Monograph of the FossilLepadidæ, Palæontographical Society, 1851.
[436]Monograph of the Fossil Lepadidæ, p. 81, pl. v.
Crustacea.—The animals whose fossil remains we have now to consider, are characterised by their crustaceous external integument or shell, which is disposed in segments, more or less distinct, the annular portions supporting articulated limbs or appendages. They are aquatic, free, locomotive beings, and possess distinctbranchiæ, or organs fitted for aquatic respiration. The Crab and Lobster are examples of those tribes in which the external crust is calcareous, and "coloured by a pigmental substance, diffusedmore or less irregularly through it; and is formed upon and by a vascular organized integument, or corium, which is lined by the smooth serous membrane of the visceral cavities." (Owen.) The subdivisions of this class have relation to the forms, combinations, and proportions of the primary rings or segments of the external crust or integument, but it will not be requisite for our present purpose to enter upon this department of the subject. It may, however, be necessary to mention, that in the normal type of Crustaceans, the integument consists of twenty-one rings or segments, which form the three regions into which the body is divided; namely, the head orcephalic, thethoracic, and theabdominal; each of which is assumed to consist of seven rings, although some of these are generally anchylosed, and form but one segment; and even the three regions are occasionally more or less blended together. The cephalic portion of the crust contains the principal organs of sense, and the commencement of the digestive apparatus, and includes the masticatory appendages. Thethoracicportion is formed of the rings to which the extremities serving for locomotion are attached: and, together with the cephalic, contains almost all the viscera. The consolidation of the rings or segments takes place most generally in the cephalic, and next in frequency in the thoracic; and but rarely occurs in the abdominal region. These animals possess organs of sight variously modified, and in some species highly complicated; some have smooth or simple eyes (stemmata), and others compound eyes, like those of insects, with distinct facets. In one grand division (calledEdriopthalmia), the eyes are sessile and immovable; in the other (Podopthalmia), they are supported upon moveable stems or peduncles. These few remarks on the organization of the recent crustaceans are required, to make our description of the fossil remains intelligible to the general reader. As the shell, or calcareous integument, even in those species in which it isvery dense and thick, is moulded upon the soft parts it envelopes, the experienced naturalist is able, from its configuration alone, to obtain certain conclusions as to the form, size, and position of the contained viscera; and, as these animals annually shed their solid case and acquire a new one, which is moulded on the soft parts, the form and relative situation of the internal organs must necessarily be faithfully represented by the external integument, even when it has acquired its greatest degree of consolidation; thus the regions of the stomach, heart, branchiæ or respiratory organs, &c. may be distinctly traced on the external shell. Hence the fossil carapaces may afford important data regarding the structure and economy of the extinct species. M. Desmarest[437]was the first naturalist who successfully applied thisphrenological methodto the investigation of the fossil crustaceans.