776. Fossil Cetacea, 777. Otolithes of Whales, 778. Brighton
Fossil Whale, 778. Zeuglodon Cetoides, 779. Fossil Ruminants,
782. Pachydermata, 785. Fossil Elephants and Mastodons, 785.
Dinotherium, 787. Cuvierian Pachydermata, 789. Teeth of Mammalia,
793. Fossil Horse, 796. Fossil Edentata, 798. Megatherium,
798. Glyptodon, 799. Mylodon, 800. Fossil Rodents, 802. Fossil
Marsupials, 803. Triassic Mammalian Teeth, 805. Fossil Mammalia of
Stonesfield, 805. Fossil Carnivora, 807. Kent’s Hole, 810. Fossil
Seals, 812. Fossil Insectivora. 812. Fossil Bats, 813. Fossil
Quadrumana, or Monkeys, 813. Fossil Ape of France, 814. Fossil
Monkey of the Sub-Himalayas, 814. Fossil Monkey of South America,
814. Fossil British Monkeys, 815. Fossil Human Bones, 815. On
collecting and developing Fossil Remains of Mammalia, 815. British
Localities of Fossil Mammalia, 818. Bone-caves in Franconia, 820.
Retrospect, 822.
Appendix to Part III., 826.
PART IV.--Notes of Excursions, in Illustration of the Mode of
Investigating Geological Phenomena, and of Collecting Organic
Remains, 827.
Chapter XX.--General Instructions for the Collection of Specimens of
Rocks and Fossils, 831.
Chapter XXI.--Excursions illustrative of the Geological Character and
Organic Remains of the Tertiary Deposits of the London Basin, 837.
Excursion to the Isle of Sheppey, 838. Excursion to Bracklesham
Bay, 844. Notes for an Excursion to examine the Tertiary Strata of
the Isle of Wight, 847.
Chapter XXII.--Notes for a Geological Excursion from London to
Brighton, 849. A Stroll from Brighton to Rottingdean, 852.
Chapter XXIII.--Geological Notes of various Places on the Line of the
Great Western Railway; illustrative of the Oolite, Lias, &c. from
London to Clifton, 859. Farringdon, 859. Swindon, 862. Caine and
Chippenham, 863. Bath and Bristol, 864. Clifton, 864.
Chapter XXIV.--Excursion to Matlock and its Vicinity, 867. Geological
Position of Matlock Dale, 871. A Walk to the Incrusting Springs,
872. Visit to the Cavern of the High Tor, 875. Geological
Formations of Derbyshire, 878. Excursion to Crich Hill, 880. Notes
for a Geological Excursion by Bonsal Valley, and Wirksworth, to
Middleton Moor and Stonnis, 894.
Chapter XXV.--Notes for a Geological Excursion to Charnwood Forest;
by Leicester, Mount Sorel, Swithland and Woodhouse, and Bardon
Hill to Whitwick, 898.
List of Dealers in Fossils and Minerals, &c. 904.
General Index, 909.
THE
MEDALS OF CREATION.
⎼⎼⎼⎼⎼◆⎼⎼⎼⎼⎼
CHAPTER XII.
FOSSIL CEPHALOPODA; COMPRISING THE BELEMNITIDÆ, NAUTILIDÆ, AND
AMMONITIDÆ.
[Illustration: Lign. 140. Fossil Sepia or Cuttle-Fish: 1/3 _nat._
(_M. D’Orbigny._)
_Solenhofen._
(Kelæno[398] speciosa. _Count Münster._)
The impression of the body, head, and arms, with their clasps.]
[398] _Kelæno_ (one of the Furies) = Acanthoteuthis (Wagner); probably
identical with Belemnoteuthis, which also has ten sub-equal arms.--_Mr.
Woodward_.
The molluscous animals named _Cephalopoda_ (from their organs of
prehension being arranged around the upper part of the body) are
the most ancient, numerous, and interesting of this division of
animated nature; and their fossil remains comprehend the most varied
and striking forms of extinct beings that occur in the sedimentary
strata, from the earliest Secondary to the latest Tertiary formations.
The living species are but a feeble representation of the countless
myriads which swarmed in the ancient seas; yet they afford important
assistance in developing the characters of the numerous extinct genera,
whose relics abound in the strata, and will continually be presented to
the observation of the collector. It is therefore necessary to enter
somewhat in detail on the structure of these beings, that the student
may obtain a correct idea of the nature of the curious fossils to which
the mineralized remains of the durable parts of these animals have
given rise, and whose origin has but lately been correctly ascertained.
The body of these mollusca is either enclosed in a shell, as in the
_Nautilus_, or contains a calcareous or cartilaginous part, as in
the _Sepia_, or cuttle-fish; they have a distinct head, and eyes as
perfect as in the vertebrate animals; complicated organs of hearing;
and a powerful manducatory apparatus, surrounded by arms serving for
prehension. They have below the head a tube which acts as a locomotive
instrument to propel the animal backwards, by the forcible ejection
of the water that has served the purposes of respiration, and which
can be thrown out with considerable force by the contraction of the
body. The figures 1 and 6, _Lign. 142_, are views of a naked (that is,
_shell-less_) cephalopod, showing the arms, eyes, and a pair of fins,
for swimming. The Cephalopoda, thus endowed with powerful organs of
locomotion, traverse the seas unrestricted, and are seen in groups of
myriads in the midst of the ocean, and only appear periodically near
the shores. Their fossil remains consist of--
1st. The external shells; which are generally symmetrical, and either
straight (as in _Orthoceras_, _Lign. 155_); arched or bent (as in
_Crioceras_, _Lign. 160_); spiral (as in _Turrilites_, _Lign. 163_); or
involute,[399] and simple (as in the _Argonaut_), or divided, by smooth
or foliaceous partitions, into chambers or air-cells, connected by a
hydraulic tube or siphuncle (as in _Nautilus_, _Lign._ 149 and 150, and
_Ammonites_, _Lign._ 156 and 157).
[399] _Involute_, as applied to the shells of Cephalopoda, implies that
the inner whorls are embraced by the outer turn or whorl; _convolute_,
the inner turns apparent, or exposed; _evolute_, the whorls coiled in
one plane, but not touching each other; _revolute_, the extremities
bent inwards.
2dly. The internal horny or calcareous support, called _osselet_, and
its appendages.[400] (_Lign. 143._)
[400] The _bone_ or _shell_ of the Cuttle-fish, the friable part of
which, reduced to powder, forms _pounce_, is the _osselet_ of that
cephalopod.
3dly. The ink-bladder, with its inspissated contents, termed _sepia_.
4thly. The mandibles of the mouth, or beaks, called _Rhyncholites_.
(_Lign. 150_, _fig._ 1.)
5thly. The soft parts of the animal in the state of molluskite;
impressions of the head and tentacula, and remains of the clasps or
curved hooks of the arms of some species (see _Lign._ 140 and 145).
These several parts are generally found separate, but they sometimes
occur in their proper relative position, and from such examples the
nature of the original may be determined.
The Cephalopoda[401] are divided into two orders, according to
the number of their organs of respiration, or gills; namely,
the _Dibranchiata_, or those which have two gills, (called also
_Acetabulifera_, from their arms being furnished with rows of little
cups or suckers;) and the _Tetrabranchiata_, which have four gills, or
branchiæ, and very numerous arms without suckers.
[401] The best systematic account of the Cephalopoda and Gasteropoda,
both recent and fossil, yet published, is contained in the first part
of the very valuable Manual of Mollusca, by Mr. S. P. Woodward, of the
British Museum.
[Sidenote: FOSSIL CEPHALOPODA]
FOSSIL DIBRANCHIATE CEPHALOPODA.
The _Argonaut_, or Paper Nautilus, whose elegant fragile shell is too
well known to require description, is the only living genus of this
Order, in which the animal is protected by a hard calcareous external
covering. This shell is symmetrical, and convoluted on a vertical
plane, and consists of but one cavity or chamber. The other genera
are naked, and possess an internal chambered shell (as in the recent
_Spirula_), or some modification of such an apparatus. The last chamber
or cell of these enclosed shells is too small to admit any part of the
body of the animal; a character by which the fossil species of this
Order may be distinguished from those of the other order. Others have
a horny or calcareous osselet, as the bone of the Cuttle-fish, and pen
of the Calamary or Sea-pen (see _Bd._ pl. 28); and in an appendage of
this kind a conical chambered shell is contained in many of the fossil
genera, hereafter to be noticed. These animals have eight arms, with
the addition in some genera of two long tentacula, which are furnished
with rows of suctorial disks or cups, called _acetabula_ (see _Lign.
142, figs. 1, 6_).
These naked Cephalopoda, devoid of any external defence, possess a very
extraordinary means of escape from their enemies. They are furnished
with a bag or bladder, containing a dark fluid resembling ink in
appearance, which they have the power of ejecting into the surrounding
water upon the approach of danger; and by the obscurity t us induced,
they foil the pursuit of their adversaries: the Nautilus and other
cephalopods, protected by a large external shell, are destitute of such
an apparatus. The deep brown colour, _sepia_, was formerly prepared
from the fluid of the ink-bags of different species of Cuttle-fish; a
similar substance secreted by extinct naked Cephalopoda, as we shall
presently demonstrate, is found in a fossil state. These preliminary
remarks on the organization of the recent animals will prepare us for
the investigation of the extinct species. We will first notice those
remarkable fossils, called _Belemnites_, or thunder-stones.
[Illustration: Lign. 141. Belemnites: 1/2 _nat._ _Chalk and Oolite._
Fig. 1.--Belemnitella mucronata. _Chalk._ _Brighton._ On the
right of the figure is a view of the aperture, and a transverse
section.
2.--Portion of a Belemnite, containing the internal conical
chambered shell, called _phragmocone_. _Oolite._
3.--Belemnitella quadrata. Beauvais, France. The quadrangular cavity
is shown in the upper figure on the left. (_M. D’Orbigny._)
4.--Belemnites dilatatus. _Lower Greensand_ (_Néocomien_). _France._
]
[Sidenote: BELEMNITES]
Belemnite (from a supposed resemblance to the head of a dart or
javelin). _Lign._ 141 to 144. Among the innumerable relics of an
earlier world, which swarm in the sedimentary deposits, there are
perhaps no fossil bodies that have excited more curiosity, and given
rise to so many fruitless conjectures as to their nature and origin,
as the Belemnites.[402] These are long, cylindrical, or fusiform
fossils, more or less pointed at one extremity, and having at the
other and larger end a conical cavity, which is either occupied by a
chambered shell, or filled up with the material in which the fossils
are imbedded. Their substance is like fibrous calcareous spar, varying
in colour from a dark brown to a light amber; many are transparent,
others nearly opaque. When broken transversely they present a radiated
structure (_Lign. 141, fig. 1_) and a minute central cavity, or axis,
is seen to extend through the whole length of the solid portion of the
stone (see _Lign. 142, fig. 5._). A longitudinal section (_Lign._
142, _figs._ 4 and 5) shows the conical cavity in the upper part, and
that the shaft consists of a series of concentric layers. Such are the
characters of these fossils in the examples of most frequent occurrence.
[402] See Park. Org. Rem. vol. iii. p. 122.
The Belemnites vary in size from the small, delicate, transparent
species, _Lign._ 142, _figs._ 3 and 4, to massy opaque specimens,
several inches in circumference, and from ten to twenty inches in
length. They present also considerable variety of form; some are
regularly cylindrical, as in _Lign. 141 fig. 1_; others broad and
flattened, as in _fig. 4_; or subfusiform, as in _Lign._ 142, _figs._ 3
and 4. The small end is slender and pointed in some belemnites, and in
others is obtuse, or rounded, with a projecting point. In many there is
a longitudinal groove or furrow on the ventral aspect; and some species
have a furrow on each side, as in that represented in _Lign. 142,
fig. 2_.
But the fossils above described are only a part of the original
structure of the Belemnite. When in a perfect state, the cavity seen in
_Lign. 142, fig. 5_, is occupied by a chambered conical shell, called
the _phragmocone_, composed of a series of shallow concave cells, of a
nacreous or pearly substance, which are pierced by a siphuncle at the
margin; see _Lign. 141, fig. 2_.
The parts of the Belemnite at present known consist of--
1st. The spathose osselet, or _guard_, having at the larger end a
conical cavity, called the _alveolus_, as in _Lign. 141, fig. 1_, and
_Lign. 142, fig. 5_.
2dly. A conical, chambered pearly shell, termed the _phragmocone_,
which is situated in the _alveolus_ (as in _Lign. 141, fig. 2_).
[Illustration: Lign. 142. Belemnites: 1/2 _nat._
Fig. 1.--A front view of the supposed animal of the Belemnite, by
_M. D’Orbigny_. _b._ denotes the osselet, to the base of which
the _Belemnite_, _a_, is attached.
2.--Belemnites bipartitus; the figure below shows the form
of the aperture. _Neocomian Formation._ _France._ (_M.
D’Orbigny._)
3.--Belemnites Listeri (G. A. M.); _from the Galt._ _Ringmer._
4.--A longitudinal section of B. Listeri.
5.--Belemnites semicaniliculatus: a longitudinal section;
the figure below is the aperture of the _alveolus_. _From the
Firestone (Craie tufeau) of France._
6.--A side view of fig. 1.
]
3dly. The horny prolongation of the _capsule_ (the outer investment of
the _guard_), called the _receptacle_, as in _Lign. 143_.
4thly. The _ink-bag_, and its inspissated fluid, _sepia_; (_Bd._ pl.
44′, figs. 7, 9.)
[Illustration: Lign. 143. The structure of the sherry parts of the
Belemnites Puzosianus.
_Oxford Clay._ _Christian Malford._ (1/4 _nat. size_.)
_a, a._ The dorsal basilar processes of the phragmocone.
_b, b._ Upward extension of the attenuated osselet.
_c._ Siphunculus.
_d._ Phragmocone: the transverse lines indicate the septa.
_e._ The capsule or outer investment of the guard.
_f._ The distal part of the phragmocone.
_g._ The alveolus or cavity in the guard.
_h._ Vertical section of the guard.
_i._ The solid part of the rostrum or guard.
_k._ The sulcus or groove on the ventral aspect of the rostrum.
_l._ Shows the continuation of the capsule, in section, continued from e.
_m._ Diverging parallel striæ observable between the dorsal processes of
the phragmocone.
_n._ Transverse section of half the diameter of the radiated structure.
]
[Illustration: Lign. 144. Very perfect specimen of Belemnites
Puzosianus.
_Oxford Clay._ _Christian Malford, Wilts._ (1/6 nat. size.)
_a, a._ Basal processes of the phragmocone.
_b._ The phragmocone.
_c._ The rostrum or guard of the osselet, containing the apex of the
phragmocone in its upper part.
]
The invariably radiated crystalline structure of the Belemnite has
evidently resulted from the peculiar organization of the original
osselet, which is formed of thin concentric laminæ, of very minute
prismatic trihedral fibres, arranged at right angles to the planes of
the successive layers.[403]
[403] The Belemnitic shell presents the same arrangement of its
constituent layers as the Pearl-mussel, Pinna, and other _Aviculidæ_,
viz. the outer layer is prismatic-cellular, the inner nacreous: the
first is formed by the free margin of the mantle, the second by the
visceral ("peritoneal") part of the mantle.--_Mr. Woodward._
From the obvious analogy of the structure above demonstrated with that
of the recent dibranchiate Cephalopoda, several eminent naturalists
inferred that the animal of the Belemnite was closely related to the
existing types; and the late Mr. Miller, in a communication to the
Geological Society of London, gave a restored figure of the original,
which, as modified by M. D’Orbigny, is represented _Lign._ 142, _figs._
1 and 6. The indefatigable and successful researches of the Rev. Dr.
Buckland have confirmed the general correctness of this restoration.
In the Lias of Dorsetshire two specimens of the Belemnite, with its
chambered shell and horny or pearly receptacle, still retaining the
ink-bag and its contents, have been discovered, and were figured in
the Br. Treatise (_Bd._ pl. 44′, 44″). A third specimen, showing the
ink-bag, is in the British Museum.
The ink-bag of the Belemnite is very small, as might be expected, from
the extent to which it is protected by a chambered shell. The mandibles
or beaks of the Belemnite are supposed to have been horny, as in the
other naked Cephalopoda; since no calcareous beaks have been found
associated with their remains.
"The Belemnite having the advantage of its dense, but well-balanced
internal shell, must have exercised the power of swimming backwards
and forwards, which it possessed in common with the modern decapod
(_ten-armed_) Dibranchiata, with great vigour and precision. Its
position was probably more commonly vertical than in its recent
congeners. It would rise swiftly and stealthily to infix its claws
in the belly of a supernatant fish, and then perhaps as swiftly dart
down, and drag its prey to the bottom and devour it. We cannot doubt
at least but that, like the hooked Calamaries of the present seas, the
ancient Belemnites were the most formidable and predacious of their
class."--Owen.
The Belemnites of the oolitic limestones frequently contain the
phragmocone, either filled with calcareous spar, or with its cells
empty. In the clays the horny sheath or receptacle is sometimes found
pressed flat and extending above the alveolus of the osselet, and has
often a thin coat of nacre of a pearly lustre, but it is more commonly
detached.
The Belemnites abound in the Lias, Oolite, and Chalk, and have not
been discovered in any other deposits; there are nearly thirty British
species, some of which are restricted to the Chalk, and others to the
Oolite and Lias.
A few characteristic forms are represented, _Lign._ 141 and 142, in
order to illustrate the three groups which, according to M. D’Orbigny,
are peculiar to the grand divisions of the Cretaceous formation.
1. Belemnitella mucronata. _Lign. 141, fig. 1._--The name
_Belemnitella_ is given to those Belemnites which have a slit, or
crevice, on the anterior margin of the alveolus or cavity, and two
lateral impressions. The surface is sometimes granulated, and often has
vascular markings, produced by the investing integument of the living
animal. The form of the aperture is shown in the middle dextral figure;
and the radiated structure, as seen by a transverse section, in the
sketch.
This species is abundant in the _White Chalk_, particularly in certain
localities in Norfolk and Devonshire. It is more frequent in the chalk
of Kent than in that of Sussex; and in the cretaceous strata around
Brighton, than in those near Lewes. I have never been able to detect
the least vestige of the phragmocone, or chambered shell, in the
alveolus. This Belemnite is occasionally imbedded in flint nodules; and
such examples possess the calcareous crystalline structure of the chalk
and limestone specimens. In the chalk of Ireland, the Belemnites which
have been corroded, or perforated by marine borers (_cliona_), are
often injected with flint; and if the calcareous substance be removed
by immersion in dilute hydrochloric acid, exquisite siliceous casts
may be obtained (see also page 403). It is not unusual to find flints
with a cavity, occasioned by the solution and removal of the calcareous
guard, and having a siliceous conical cast of the alveolus, occupying
the upper part of the interspace. The reader will recollect that the
pulley-stones of the Derbyshire Encrinites were produced by a similar
process (see p. 285, vol. i.).
The American cretaceous sands abound in a species of Belemnitella,
nearly related to _B. mucronata_.
2. Belemnites Listeri. _Lign. 142, fig. 3._--This small elegant
Belemnite has two lateral grooves, and is generally as transparent as
amber; it has frequently a nacreous or calcareous pellicle partially
investing the guard. It seldom exceeds two inches in length. It is
abundant in, and peculiar to, the Galt, or blue marl of the Chalk, and
is constantly associated with the Inocerami, previously described as
common at Folkstone, Bletchingley, Ringmer, and other localities of
that deposit. The Red Chalk of Norfolk contains the same species (_Min.
Conch._ tab. 589).
3. Belemnites dilatatus. _Lign. 141, fig. 4._--This species is
distinguished by its flattened form, and by the longitudinal furrow
being situated on the margin opposite to the siphuncle of the
phragmocone, instead of being on the same side, as is most usual. It is
supposed by M. D’Orbigny to be characteristic of the Neocomian beds, or
lowermost division of the Shanklin Sand.
4. The Chalk-marl contains a Belemnite of a more elongated form than
those above described, the apex gradually tapering to a point, with a
slight double furrow on each side. It is named _B. lanceolatus_ (_Sow.
Min. Conch._ tab. 600, figs. 8, 9), and is very common in the marl-pits
at Steyning, Clayton, and Hamsey, in Sussex.
At the base of Golden Cap Hill, near Charmouth, there are two strata
of marl-stone observable on the shore, which are literally paved with
Belemnites. Great numbers of these fossils have Serpulæ and other
extraneous shells attached to them, a proof that the ink-bags and other
soft parts of the mollusks had decomposed, and that the guards had lain
uncovered at the bottom of the sea.
M. De Koninck has discovered in the Devonian limestone of Belgium, at
Couvin and Visé, a small fossil body which closely resembles in form
and structure the rostrum or guard of a belemnite; it is, however, too
fragmentary to admit of positive detemination.[404]
[404] Bulletin del’Académie Roy ale de Bruxelles, tome x. No. 3. p. 207.
[Sidenote: BELEMNOTEUTHIS]
Belemnoteuthis[405] (J. C. Pearce). _Lign. 145._--Within the last few
years much additional knowledge has been obtained regarding the nature
of the extinct Cephalopoda, by the discovery in the Oxford clay, at
Christian Malford, not only of several examples with the receptacle and
ink-bag in their natural relative positions, but also with the remains
and impressions of the mantle, body, tentacula with their hooks, and
the fins!
[405] For the history of this interesting Cephalopod consult Phil.
Trans. 1848, and 1850; Ann. Nat. Hist. June 1850; Petrif. p. 459, &c.
[Illustration: Lign. 145. Belemnoteuthis antiquus. (_Pearce._)
_Oxford Clay._ _Christian Malford._ (1/2 _nat. size_.)
_a._ The uncinated arms and tentacles.
_b._ Remains of the head and eyes.
_c._ The mantle, with indications of fins.
_d._ The pigmental sac or ink-bag.
_e._ The osselet: the transverse lines indicate the septa of the
phragmocone, which is covered by a horny sheath or capsule.
_f._ The solid terminal apex of the osselet.
]
[Sidenote: BELEMNOTEUTHIS ANTIQUUS]
Certain argillaceous strata of the Oolite, as well as of the Lias,
appear to have been peculiarly favourable for the preservation
of the muscular tissue and integuments, and in many specimens of
Belemnoteuthis, the arms, the large sessile eyes, the funnel, a great
proportion of the muscular parts of the mantle, remains of the two
lateral fins, the ink-bladder and duct, and the phragmocone, are well
displayed, as in the beautiful example, _Lign. 145_, for the drawing
of which I am indebted to S. P. Woodward, Esq., of the British Museum.
(See also _Lond. Geol. Journ._ pl. xv. and xvi.)
[Illustration: Lign. 146. Horny rings and hooks of Belemnoteuthis
antiquus.
Fig. 1, 3.--Detached hooks (_natural size_).
2.--Three hooks with attached horny rings: from a specimen in
the possession of Mr. Cunnington.
4.--Part of one of the arms, showing four hooked spines.
5.--Transverse section of the distal part of the osselet of
Belemnoteuthis, exposing the apex of the chambered shell in
the centre, surrounded by the radiated osselet, _a_
(_magnified four diameters_).
]
From the extraordinarily perfect condition of the Belemnoteuthis
here figured, which of itself exemplifies the essential parts of
its structure, a brief description will suffice. The body is of an
elongated form, with a pair of lateral fins, two large sessile eyes,
eight uncinated arms, and a pair of armed tentacles; each arm was
furnished with from twenty to forty pairs of hooks, placed alternately.
Like the Sepia it had a pigmental sac or ink-bag, which is generally
found filled with the inspissated secretion. The inferior part of the
body is of a conical form, and contains a brown horny osselet, with a
siphunculated phragmocone, that terminates in a guard or rostrum of a
fibrous structure.
[In the recent genus _Onychoteuthis_, the tentacles alone are armed
with claws; _Enoploteuthis_ has claws both on the arms and on the
tentacles, but the latter are long and feeble, and the hooks are
confined to their extremities. The extinct _Belemnoteuthis_ (like the
_Acanthoteuthis_ of Solenhofen, _Lign. 140_) had eight nearly equal
arms, the dorsal pair being rather smaller than the rest; each arm
was furnished with twenty to forty pairs of hooks, forming a double,
alternating row. The tentacles were not longer than the arms, and like
them had a double series of hooks extending from their bases to the
points. In all essential points of structure, the Belemnoteuthis is
most nearly related to the Calamaries (_Teuthidæ_), but, in consequence
of the prolongation of its pointed shell posteriorly, the fins
become lateral (as in _Sepiola_ and _Sepia_), instead of terminal.
Whilst the complicated (chambered) structure of its shell, and the
peculiar character of the _tentacles_, show that it must be regarded
as a type distinct from and equal in importance to the Calamaries.
It cannot be doubted that the _Belemnite_ and _Conoteuthis_ present
similar conditions of the soft parts; and the four genera will form
the Family Belemnitidæ. The normal position of these animals in the
sea is horizontal, whilst that of the Nautiloid genera must have been
vertical, with the head downwards.--_Mr. Woodward._]
The fossils which have afforded this unexpected and highly interesting
illustration of the nature of the extinct animals of this Order
have been obtained by closely examining the shales in which they
abound, and, before removing the solid osselet, carefully searching
the surrounding stone for traces of the more perishable parts. The
attention of the collector can scarcely be too often directed to the
necessity of examining the surrounding matrix before extricating a
fossil from its bed.
[Illustration: Lign. 147. Osselets of extinct dibranchiate Cephalopoda.
(_Woodward_, _Manual_, p. 76, pl. 1 & 2.)
Fig. 1.--Belosepia sepioides; 1/2 _nat._ _Eocene._ _Bracklesham._
2.--Spirulirostra Bellardii; 2/3 _nat._ _Miocene._ _Turin._
3.--Beloteuthis subcostata; 1/4 _nat._ _Lias._ _Wirtemberg._
4.--Beloptera belemnitoides; 2/3 _nat._ _Eocene._ _Bracklesham._
]
[Sidenote: BELOPTERA]
Beloptera. (_Bd._ pl. xliv. _fig._ 15. _Min. Conch._ tab. 591.)--Under
this name Mr. Sowerby figures and describes a very curious fossil, from
the London Clay at Highgate, which seems to hold an intermediate place
between the Cuttle-fish and the Spirulirostra. The guard, which is of
an oblong form, with an obtuse apex, has the structure of the osselet
of the Sepia, and contains in its upper part a phragmocone, the cells
of which are very narrow. In strata of the same age, in France, three
species have been discovered by M. Deshayes. I allude to these shells,
that the attention of the collector may be directed to the search after
other examples in our tertiary deposits.
Fossil Calamary, or Squid. Geoteuthis.[406] (_Bd._ pl. xxviii.
xxix.)--The common Calamary (_Loligo vulgaris_) is so often seen on our
shores, that its general aspect must be familiar to all who frequent
the sea-side. In this animal, the osselet, or internal support, is a
cartilaginous elongated body, which, from its form, is called Sea-pen
(_Bd._ pl. xxviii.); and even this delicate structure is found in
a fossil state. In the Lias of Lyme Regis, Miss Mary Aiming first
discovered specimens of _Sea-pens_ in juxtaposition with the ink-bag,
as in the recent Calamary; and subsequently many similar examples
have been found, both in England and on the Continent. Dr. Buckland
has given some exquisite figures of these fossils; and his collection
contains a matchless series of these most interesting organic remains.
In some specimens the ink-bag and its tube or duct, but little
compressed, are occasionally met with, having a brilliant nacreous
pellicle, the remains of the sheath, attached to the surface. The
ink-bag is sometimes of considerable magnitude; specimens have been
found at Lyme Regis nearly a foot in length.[407] The circumstance of
the ink-bags being generally full of sepia admits of the inference (as
Dr. Buckland with his wonted acumen remarks), that these individuals
died suddenly; for their living analogues reject the inky fluid
upon the least approach of danger. The perfect condition of the bag
proves also their instantaneous enclosure in the deposit, for the
distended membrane would otherwise have burst from decomposition,
and the contents would have escaped. The fossil marine reptiles, the
Ichthyosauri, &c., with which these fossils are associated, present
similar phenomena, as we shall hereafter have occasion to remark, and
strengthen the probability, that swarms of the inhabitants of the
Liassic ocean were suddenly destroyed, and imbedded, on the area now
occupied by their remains.
[406] Geoteuthis has hooks on its arms; hut, being a Calamary
(_Teuthid_), it would probably have unequal arms.--_Mr. Woodward._
[407] The large ink-bags figured by Dr. Buckland (Br. Tr. vol. i. pp.
372-379, pl. xliv′.) belonged to the great Geoteuthis Bollensis, of
Schuble.--_Mr. Woodward._
In the cream-coloured limestone, of Solenhofen, so rich in organic
remains of the highest interest (_Wond._ p. 578), the soft parts
of naked Cephalopoda have also been discovered. I have figured,
_Lign. 140_, a beautiful specimen obtained by the late Count Münster,
which exhibits an imprint of the body, the arms and tentacles being
represented by ten double rows of horny hooks, which precisely resemble
those of Belemnoteuthis. M. D’Orbigny supposes that the original animal
closely resembled a recent decapod called _Enoploteuthis leptura_.
[Illustration: Lign. 148. Fossil Shells related to the Argonaut.[408]
Fig. 1.--Bellerophon costatus. _Mt. Limestone._ _Yorkshire._
2.--Bellerophon bilobatus. _Sil. Syst._
[408] Some naturalists consider the Bellerophon to be allied to the
Carinaria (_Heteropod_).
]
Bellerophon.--It has been already stated, that the animals of one
genus of the existing dibranchiate Cephalopoda are protected by a
thin, flexible, symmetrical, keeled shell, convoluted on a vertical
plane, and having but one chamber--this is the _Argonaut_, or _Paper
Nautilus_, an inhabitant of the Mediterranean. This animal belongs
to the Octopoda, or those which have eight arms; and in one pair of
these processes the extremities expand into broad and thin membranes,
by which the delicate, elastic, calcareous envelopement, or shell,
is secreted. There membranes usually encompass the shell, and meet
and overlap each other along its keel; and by them chiefly the shell
is retained in its position. When these membranes are withdrawn, or
the animal dies, the shell, having no muscular connexion with the
soft parts, readily separates from the body. Hence the doubts so long
entertained as to the relation between the animal of the Argonaut and
its shell, but which are now set at rest; the observations on the
living animal by Madame Tower, and the anatomical demonstrations by
M. Sander Rang, having removed the obscurity in which the subject was
formerly involved.
In the Silurian, Devonian, and Carboniferous deposits there are
several species of a genus of shells, the animals of which are by
some considered to have been analogous to the recent Argonaut. It is
named Bellerophon. I have figured two species; one from the Mountain
Limestone, _Lign. 148, fig. 1_; the other from the Silurian System.
There are about thirty British species, most of which are of small
size; some of them are keeled, others have a slight dorsal depression,
as in _fig. 1_. and many have the back rounded, and the sides lobed, as
in _Lign. 148, fig. 2_ .
FOSSIL TETRABRANCHIATE CEPHALOPODA.
I am not aware of the existence of any British fossils analogous to
Spirula (_dibranchiate_); for the minute fossil polythalamia, formerly
referred to this class, are now known to have belonged to animals
possessing an organization altogether different, as we have already
explained (see p. 369). I therefore proceed to notice the fossil
remains of those _Cephalopoda_ which were furnished with an external
shell having its cavity divided by cells, which are perforated by a
hydraulic tube or siphuncle; and of which group the recent Nautilus is
the type.
[Illustration: Lign. 149. Nautilus pompilius in its shell.
_a._ The animal, occupying the last or body chamber of the shell.
_b._ The shell cut vertically through the middle, and showing the
air-chambers and the siphuncle.
]
The appearance and structure of the recent shell are familiar to
every one; a correct knowledge of the nature of the original animal
has, however, been obtained but very recently. In its general
characters the animal of the Nautilus, which is an inhabitant of the
seas of hot climates, resembles the naked Cephalopoda; it possesses
four _branchiæ_, or gills, and numerous hollow arms and retractile
tentacula. Its head is furnished with a muscular flattened disk, which
serves as an operculum to the shell when the animal is retracted. The
beaks are horny, and coated at their tips by calcareous matter. It has
no ink-bag, and is destitute of fins or other organs for swimming. The
body occupies the ample outer cell of the shell, to which it is firmly
attached by two lateral muscles; and it has a siphuncle, that passes
from the posterior part of the animal through the shelly tube, and by
which communication is maintained with the entire series of cells or
chambers. The siphuncle is provided with a small artery and vein, and
traverses the entire series of chambers, thus maintaining the vitality
of the shell. Mr. Edwards considers that "it may be looked upon as an
elongated cæcum, and that it is not under any circumstances used by the
animal as a hydrostatic balance."[409]
[409] The reader interested in this subject should consult the
_Memoirs_ by M. Valenciennes, Mem. de l’Inst.; M. Vander Hoven, in the
Proceedings of the Zoological Society; Prof. Owen’s _Memoir on the
Pearly Nautilus_, Mr. Gray’s paper in the An. Nat. Hist., Mr. Edward’s
Monograph in the Palæont. Soc., and Mr. Woodward’s _Manual_.
Upon making a vertical section of the shell, the inner volutions
are exposed, and the cavity is seen divided at regular intervals
into cells, by smooth, concave, nacreous septa; these vary in number
according to the age of the individual; there are about thirty-five
in an adult specimen. The partitions are pierced in the _centre_ by
a shelly tube, which traverses each cell to within a short distance
of the next partition; and this tube is rendered a continuous channel
in the living animal, by the membranous siphuncle. This series of
air-chambers constitutes an apparatus which renders the Nautilus nearly
of the same specific gravity as the surrounding water, and enables
it to rise to the surface of the sea, or sink to the bottom, by a
very small amount of muscular exertion. The Nautilus swims, like the
Cuttle-fish, by expelling the water from its respiratory chamber; the
walls of which are very thick and powerful muscles.
From this very general description of the only living representative
of the numerous genera of tetrabranchiate Cephalopoda, which swarmed
in such prodigious numbers in the ancient seas, we may pass to the
consideration of the fossil Nautili, and their related congeners. Our
remarks must be limited to the genera that will serve to demonstrate
the most important modifications of structure, and explain the nature
of the fossil remains of this extensive class of extinct beings.
The genera into which these shells are distributed are founded upon
the mode in which the shell is coiled, its form, the character of the
partitions or septa, and the situation of the siphuncle. A little
reflection will enable the student to understand the principles of
this classification. The essential character of all the shells of this
class, is to have an external chamber larger than the inner chambers,
and which contains the body of the animal; to be divided internally
into different compartments, by partitions (concavo-convex, with the
concavity outwards); and to have a pipe or tube extending from the
outer open chamber to the innermost cell. They are divided into three
groups or families.
1. The Nautilidæ (_Bd._ pl. xxxi.): in these the septa are smooth, or
but slightly undulated, and the siphuncle either traverses the centre
of the cell-partitions, or is situated towards the inner margin or turn
of the spire.
2. The Orthoceratidæ (_Lign. 155_): in these the siphuncle is
complicated in its structure; it is central or lateral; the septa are
smooth. (_Woodward’s Man. Moll._ p. 87.)
3. The Ammonitidæ (_Bd._ pl. xxxv-xlii.): in these the septa are
more or less waved, and their margins foliated or crenated, that is,
indented; and the siphuncle is situated at or near the outer margin.
In the Nautilus, the shell is convoluted on the same plane, in spiral
whorls, all of which are contiguous, and the siphuncle is central.
The British strata contain about sixty species of Nautili. The
Tertiary formations have yielded five or six; the Cretaceous a like
number; the Lias and Oolite ten or eleven; the Carboniferous about
thirty species; and the Devonian two species. In the London Clay a
large and beautiful species is abundant (_Nautilus imperialis._ _Min.
Conch._ tab. i.), having the shell very commonly entire; but the outer
opaque coat frequently flakes off, and exposes the pearly or nacreous
internal layer. The septa generally retain their original nacreous
structure, and the cells are either occupied by clay or marl, or are
partially filled or lined with calcareous spar, brilliant pyrites, or
other mineral matter. These Nautili are often found constituting the
nuclei of the _septaria_, or clay nodules, with which this deposit
abounds.[410] The small species, _N. centralis_ (_Ly._ _fig._ 179),
and _Nautilus_ (_Aturia_) _ziczac_ (_Wond._ p. 247), occur in the same
strata. The London Clay of the Isle of Sheppey and of the coasts of
Hants and Sussex is productive of these fossils.
[410] Three other well-marked species are figured and described by Mr.
Edwards (Monog. Pal. Soc.) from the English eocene strata: viz. _N.
Sowerbyi_, _N. urbanus_, and _N. regalis_.
[Illustration: Lign. 150. Fossil Nautili. _Chalk marl._
Fig. 1.--Beak of a Nautilus, (_Rhyncolite._) Back view.
1_a_.--Anterior view of the same.
1_b_.--Profile of the same.
2.--Vertical section of Nautilus pseudo-elegans. _Hamsey._
_a._ The siphuncle.
3.--Front view of N. Deslongchampsii. (_M. D’Orbigny._) _Hamsey._
3_a_.--Lateral view of the same.
]
In the White Chalk near Lewes, casts of several very large Nautili
have been found; but shells of this genus are more abundant in the
lower division, the _Chalk-marl_. A large and beautiful species,
_Nautilus elegans_ (_Min. Conch._ tab. 116), is not unusual in the
marl-pits near Lewes, Clayton, Steyning, &c. and may be considered as
characteristic of that portion of the Cretaceous deposits. The first
specimen discovered (_Foss. South D._ tab. xx) was from the marl-bank
immediately at the foot of the mound on which stands the church of
Hamsey, a little hamlet on the north of Lewes; a spot from which I
obtained numerous other cephalopodous shells, at that time unknown as
British species. The collocation of fossils at Hamsey is similar to
that observable in the quarries at St. Catherine’s Mount, near Rouen.
These remains only occur as casts, no vestige of the shell remaining;
but sections will sometimes show the situation of the siphon, its tube
being filled with a different material from that which occupies the
cells. This is exemplified in the section of a smaller species (_N.
pseudo-elegans_, _Lign. 150, fig. 2_), in which the channel of the
siphon is filled with a dark-coloured marl, _a_; the lines formed by
the section of the smooth septa are also shown. In the same lignograph,
_fig. 3_, a front view and profile of another chalk-marl Nautilite are
figured.[411]
[411] The student will find a section of the shell of the recent
Nautilus a very instructive object of comparison, in the investigation
of the fossils of this family.
[Illustration: Lign. 151. Nautilus elegans.
_Lower Chalk._ _Lewes._ (1/6 _nat. size_.)]
[Illustration: Lign. 152. Nautilus Saxbyi. _Lower Greensand._]
In the Chalk, as well as in many other calcareous deposits, the shells
of the Nautili, Ammonites, &c. are very rarely preserved; even the
internal septa are often dissolved, and the stony casts, moulded in the
cells, remain distinct, and readily separate (_Lign. 153_). An entire
series, from the innermost cell to the outer chamber, may sometimes be
obtained (in the Coralline Oolite); forming, as it were, a dissected
model of the internal structure.[412] The beaks or mandibles are
occasionally found fossil (_Lign. 150, fig. 1_).
[412] _Bd._ pl. xlii. _fig._ 1: see also plates xxxi. to xliii., for
illustrations of Nautilites.
[Illustration: Lign. 153. Casts of chambers of Nautilus and Ammonite.
(1/2 _nat._)
Fig. 1.--Cast in calcareous spar of a chamber of Nautilus.
_From the London Clay._
2.--Cast of a chamber of Ammonites excavatus.
_From the Coral Rag._
]
[Illustration: Lign. 154. Clymenia: 1/2 _nat._ _Devonian._
Fig. 1.--Clymenia Sedgwickii.
2.--Front view of the same.
3.--Vertical section of C. striata, showing the siphunculus on
the inner edge of each septum.
4.--Suture of C. striata.
]
Clymenia (_Lign. 154_, _Ly._ _fig._ 406).--This genus belongs to the
Nautilidæ, and is peculiar to the Devonian deposits. It differs from
the allied genera in the siphuncle being situated on the inner margin
of the septa. The shell is discoidal, and the septa are very slightly
lobed. At Elbersreuth, near Bareuth, in the N. E. of Bavaria, the
Devonian strata abound in these shells; thirty-five species have been
found, the greater number being peculiar to that locality.
In England they are chiefly found at South Petherwin, Cornwall, and in
the Devonshire marbles. (_See Phillip’s Pal. Foss. Devonshire._)
[Sidenote: ORTHOCERAS.]
Orthoceras (straight shell), _Lign. 155._--The shells of this genus
may be described as Nautili uncoiled and extended in a straight line.
They are straight, elongated, chambered shells, with smooth and gently
undulated septa, which are concave towards the opening or upper part,
and have the siphuncle either central, or not far removed from the
centre. The _Orthoceratites_ more especially belong to the ancient
Secondary strata. They first appear in the Silurian, and abound in
the Devonian and Carboniferous. They vary in size from a few inches
to several feet in length, and eight or nine inches in diameter; and
in form, from a slender elongated cone, to a short, massy, almost
spherical figure, with a contracted orifice. Some examples have been
noticed with upwards of sixty cells. Mr. Sowerby figures and describes
_O. giganteum_ (_Min. Conch._ tab. 246), from Scotland, as exceeding
seven or eight feet in length; and I discovered on the beach at
Brighton, where it had probably been brought by some vessel, among
ballast, a fine fragment of the same species, indicating as great
a magnitude. Several species are figured, _Lign. 155_, to show the
structure and appearance of these fossils. The casts of the separate
cells are often found. The section, _fig._ 3, from the red marble of
Devonshire, beautifully displays the situation of the siphuncle, and
the lines of the septa. The shelly siphuncle, which is moniliform
(_bead-like_), or dilated at each chamber, is replaced by white spar;
and the membranous internal tube is filled with a dark substance,
probably molluskite.
[Illustration: Lign. 155. Orthoceratites.
Fig. 1.--Orthoceras striatum. (_Min. Conch._) _Devonian._
2.--Orthoceras conicum. _Whitby._ _Carboniferous._
3.--Vertical section of an _Orthoceras_, showing the central
siphon, and the chambers. _Devonshire._
4.--Orthoceras laterale. _Carb._ (_Min. Conch._)
5.--Orthoceras gregarium. (_Munch. Sil. Syst._)
_a._ One of the septa.
_b._ A portion covered at the upper part by the shell.
_c._ The lower part of the same specimen, displaying the septa.
]
There are some species in which the internal tube, as well as the
external, is calcareous, and the two are connected at regular
intervals, by radiating, hollow processes. These Orthoceratites have
been principally obtained from the Silurian limestones, at Lake Huron;
they also occur in Ireland. Mr. Stokes, who first investigated their
structure, has arranged them in a distinct genus, with the name of
_Actinoceras_ (_radiated-horn_).[413]
[413] See Geol. Trans, second series, vol. v. p. 708.
Slabs of reddish Devonian limestone, containing Orthoceratites, may be
seen in some of the pavements at Hampton Court, and in Chelsea College,
which when wet present excellent sections of the enclosed shells.
[Illustration: Lign. 156. Ammonites from the Cretaceous Formation.
Fig. 1--Ammonites varians. _Chalk-marl._ _Hamsey._
2.--Ammonites Dufrenoyi.
2_a_.--Shows the keel and septum of the same.
3.--Ammonites lautus. _Galt._ _Folkstone._
3_a_.--Keel and septum of the same.
]
Ammonitidæ.--The Ammonites, or _Cornua Ammonis_ (so called from a
supposed resemblance to the horns engraven on the heads of Jupiter
Ammon), are among the most common and well-known fossils of the British
secondary strata. In some districts, as in Yorkshire and Somersetshire,
where the Ammonites abundantly prevail, they were noticed in very
remote times. Local legends, ascribing their origin to swarms of snakes
turned into stone by the prayers of some patron saint, are still
extant, and are perpetuated by the name of snake-stones, by which these
fossils are provincially known. The Lias, near Whitby, in Yorkshire,
contains immense numbers of two or three species, one of which (_Am.
bifrons_) is figured in _Lign. 127, fig. 7_, and another in _Lign.
157_.
[Illustration: Lign. 157. Ammonites communis.
_Lias._ _Whitby._]
The shells comprehended in this family are either spiral, involute,
arched, or straight; their septa are deeply lobed, and have the margins
foliated. The siphuncle is dorsal, as shown by the notch in the cast,
_Lign. 156, fig. 3a_. Several hundred species have been described;
they are divided into genera which are characterized by essential
modifications in the direction of the spire, and the inflections of the
septa. Thus, in the _Ammonites_, _Lign. 156_, the spire is involute,
and all the turns contiguous; in _Crioceras_ (_curved-horn_), _Lign.
160, fig. 2_, evolute; in _Scaphites_, incurved at both extremities,
_Lign. 162_; _Hamites_, bent like a siphon, or hook, _Lign. 161,
fig. 1_; _Turrilites_, spiral, round a vertical axis, _Lign. 163_;
and in _Baculites_, straight, _Lign. 161, fig. 2_. New genera are
continually being added, to embrace modifications of structure which
appear to be too important for specific distinctions. I will endeavour
to render this arrangement more clear to the student by the following
definitions.
A straight tube, or horn, of an elongated conical figure, tapering to
a point, and having its cavity divided by transverse partitions, which
septa are not straight, but undulated, and their edges, which fit into
the walls of the tube, deeply wrinkled, and the whole series pierced
by a pipe running along near the outer margin, would be the model of
the shell termed _Baculites_, _Lign. 161, fig. 2_, (_Bd._ pl. xliv.
_fig._ 5;) which may be regarded as a straight Ammonite. A similar
shell, gently arched or curved, would be a _Toxoceras_, _Lign. 160,
fig. 1_; the same tube, bent upon itself, like a siphon, into unequal
limbs, not contiguous, a _Hamites_, _Lign. 161_ (_Bd._ pl. xliv.
_fig._ 10); bent and approximate, or anchylosed in a straight line,
_Ptychoceras_, _Lign. 161, fig. 4_; partially convoluted, the whorls
contiguous, and the free end recurved, _Scaphites_, _Lign. 162_; the
same form, but the spire not contiguous, _Ancyloceras_, _Lign. 160,
fig. 3_; spirally twisted around an axis, _Turrilites_, _Lign. 163_
(_Bd._ pl. xliv. _fig._ 14); coiled, but the turns not touching each
other, _Crioceras_, _Lign. 160, fig. 2_; lastly, coiled up in the
form of a disk, all the turns being contiguous, _Ammonites_.
[Sidenote: AMMONITE.]
Ammonites. _Lign. 156, 157, 158._--Shell discoidal, more or less
compressed, whorls of the spire contiguous, and often visible; septa
lobed, their margins deeply sinuated; aperture symmetrical, border or
lip thickened, often notched and auriculated. Siphuncle dorsal.
The student will be able readily to distinguish Ammonites from Nautili
by attention to the above definition. The situation of the siphuncle,
the foliated or wrinkled edges of the septa, as shown in the cast,
_Lign. 156, fig. 2_; and when these characters are wanting, the
arched ribs and elevations, as in _figs._ 1 and 3, will serve as
discriminating features. Like the fossil Nautili, the Ammonites most
commonly occur as casts, the shell having been dissolved. Sometimes
these consist of semi-transparent calcareous spar, the cast of each
cell being distinct, but held together by the interlocking of the
foliations of the septa; such examples are of great beauty and interest
(see _Bd._ pl. xlii. figs. 2, 3); they most frequently occur in the
limestones of the Oolite. The siphuncle is often preserved, even in
the chalk specimens, in which all traces of the shell are lost. In a
large Ammonite from, near Lewes, not only the shelly siphuncle remains,
but even the internal membranous tube, converted into dark molluskite.
Separate portions of similar siphuncles occur in the chalk, and have
been mistaken for tubular shells.
[Illustration: Lign. 158. Ammonites Jason. 1/2 _nat._
_Oxford Clay, Trowbridge, Wilts._
_a._--Lateral processes of the margins of the aperture.]
The outer lip, or margin of the aperture, is occasionally found entire.
In some species there is a dorsal process, as in a very common Chalk
Ammonite (_A. varians_, _Lign. 156, fig. 1_), which extends far
beyond the margin; in other species, from the Oxford Clay, there are
long, narrow, lateral appendages, (_Lign. 158_). In the collection of
S. P. Pratt, Esq., there is a small Ammonite, from the Inferior Oolite
of Normandy, in which these processes meet over the aperture, leaving
only a circular aperture towards the back of the shell (where the
siphuncle of the animal would be situated) and a narrow fissure on the
side next the involute spire. The specimen is unique, and can scarcely
be regarded as a normal form.[414] (Mr. Woodward.)
[414] M. Steenstrup has described a species of _Purpura_, which at
the close of its life shuts up the aperture of its shell, with the
exception of the respiratory siphon.--_Mr. Woodward._
From the small size of the cells of the Ammonites, particularly in
those species which are of a depressed or flattened form, it was
long doubted whether the outer chamber could have been sufficiently
capacious to contain the body of the animal; and it was supposed that
these shells were internal, like the recent _Spirula_, or _Crosier_.
But Dr. Buckland has clearly demonstrated, that the outer cell of the
Ammonite, if restricted in breadth, is sufficiently ample in length to
have contained the soft parts of a Cephalopod, equal in magnitude to
the largest known specimens, its proportion to the chambered part being
as considerable as in the Nautilus. The outer chamber often occupies
more than half, and in some instances the entire circumference of the
outer whorl (see _Bd._ pl. xxxvi.).
In certain argillaceous deposits, as the Galt, and the clays of the
Lias, Ammonites with the shell preserved are abundant; generally
the outer opaque layer is wanting, or adheres to the matrix when a
specimen is removed, leaving only the internal nacreous, or pearly
coat. Folkstone, on the coast of Kent, is celebrated for examples of
this kind, which may easily be collected from the Galt, which forms
the base of the cliffs, at Eastware Bay. Watchett, in Somersetshire,
is equally rich in the pearly Ammonites of the Lias; entire layers of
these beautiful organic remains occur in the limestones and in the
shale exposed at low water.[415]
[415] A splendid group of these Ammonites may be seen in the Gallery of
Fossils at the British Museum.
The shell of the Ammonite is generally thinner and more delicate than
that of the Nautilus. However thin these shells may be, they are
possessed of great strength of structure. Not only is the shell one
continuous _arch_, but it is moreover provided with transverse arches
or corrugated _ribs_, which, like the flutings on metal pencil-cases,
and _corrugated sheet-iron_, greatly strengthen the thin material.
These ribs are further subdivided, so as to multiply supports as the
convexity of the shell enlarges, in a manner somewhat similar to the
_groin-work_ of vaulted roofs. The spines, tubercles, and bosses, which
often arise from the ribs, are so many additions to the strength of
the latter. The sides of the shell are also supported by the transverse
plates forming the _septa_, or divisions of the chambers, and, as
these plates are very sinuous where they meet the sides of the shell,
they distribute their support over a considerable portion of the
surface.[416] These complicated edges of the _septa_ form the delicate
and intricate lines of foliation (_sutures_) seen on the casts of
Ammonites (_Lign. 156, fig. 2_), Baculites (_Lign. 161, fig. 3_),
Hamites, &c. In some species the shell is thick and dense, as in the
Ammonites of the Kimmeridge Clay near Aylesbury, in which one species
(_Ammonites biplex_, _Min. Conch._ pl. ccxciii.) in particular abounds,
and is very generally invested with the shell, as perfect as if recent.
The same Ammonite occurs in the Portland limestone above, in the state
of casts, without any vestige of the shell. In some strata the shell is
replaced by calcareous spar; in others by silex or flint.[417] In the
pyritous clays and shales of the Lias, the shell and all its delicate
internal mechanism are coated with or replaced by brilliant sulphuret
of iron, forming the most exquisite natural electrotype imaginable.
Polished vertical sections of these fossils often exhibit the inner
cells filled with transparent white calcareous spar; sometimes with
groups of crystals of sulphate of lime. The Ammonites of the Galt,
and of the Kimmeridge Clay, are also frequently imbued with the same
mineral.
[416] See Bd. i. p. 339, &c.
[417] See an admirable figure of a chalcedonic specimen, exhibiting the
foliated septa of an Ammonite, _Bd._ pl. xli.
There are about two hundred identified species of Ammonite in the
British strata, ranging through all the secondary formations; they have
not been found in the Tertiary deposits. They vary in size from half an
inch to four feet in diameter.[418]
[418] I have seen imprints of the large Chalk Ammonite, _A. peramplus_
(Min. Conch. pl. ccclvii.), on the shore off Rottingdean, and Beachy
Head, which indicated even larger proportions.
Certain species are restricted to particular formations, and are
therefore oftentimes of essential aid in determining the relations of a
deposit; for example, the _Galt_ contains several species not found in
the upper division of the Chalk; and in the Chalk-maid are species that
have not been discovered in other strata. Certain Ammonites of the Lias
are peculiar to that formation (as _A. Walcottii_, _Lign. 127, fig.
7_, p. 397; and _A. communis_, _Lign. 157_). Ammonites of species allied
to those of our Middle and Lower Oolites have been discovered in strata
in the Himalaya mountains, several thousand feet above the level of the
sea.
[Illustration: Lign. 159. Goniatites. _nat._
_Carb. Syst._
Fig. 1.--Goniatites Listeri.
2.--Goniatites striatus.
3.--Outline of a suture of _Goniatite_.
4.--Outline of a suture of _Ammonites venustus_.
The _Arrows_ in figs. 3 and 4 denote the direction of the dorsal line.
]
[Sidenote: GONIATITES. CERATITES. CRIOCERAS.]
Goniatites, _Lign. 159._--From the numerous family of Ammonites, a
separation has been made of a large division, in which the margins
of the septa are not deeply notched or foliated, and are destitute of
lateral crenatures or denticulations, so that their outline always
presents a continued uninterrupted line. The siphuncle is relatively
small. The last or outer cell of the shell extends beyond one turn
of the chambered part. The back is occasionally keeled, but in most
species is round. In illustration of this genus, which is named
_Goniatites_, I have selected two common species (_Lign. 159_) from the
Carboniferous limestone, and annexed outlines of a suture (the edge of
the septum) of a Goniatite, and of an Ammonite, for comparison. The
importance of the separation of this type of Ammonites into a distinct
genus, relates to the Goniatites being restricted to some of the older
sedimentary strata; for although there are sixty British species, none
of them have been observed above the Carboniferous system.[419]
[419] _G. Henslowi_, _G. striatus_, and _G. sphæricus_, are figured in
_Bd._ pl. xl.
In Ceratites the sutures are more simple than in the Ammonite, being
lobed rather than foliated; and the alternate lobes have their edge
crenulated or finely toothed. (_C. nodosus_, _Bd._ pl. xl.) This genus
is found in the Muschelkalk and the Keuper formations of Europe and
Asia.
Our limits will not permit us to extend this notice of the very
numerous family of Ammonitidæ,[420] except to offer a few illustrations
of some of the modifications in form to which we have already alluded,
and which will assist the student in discriminating these fossil
remains.
[420] For further information, Dr. Buckland’s Treatise, and the
respective articles in the Penny Cyclopædia, may be referred to. Mr.
Woodward’s Manual should be consulted for the classification of the
family, and M. D’Orbigny’s Paléontologie Française for the illustration
of species.
Crioceras (_coiled-horn_), _Lign. 160, fig. 2._--This shell differs
from the Ammonites in the turns of the spire being distant from each
other. The siphuncle is continuous, and the septa are regularly divided
into six lobes. I have found specimens of this genus in the Chalk-marl
at Hamsey, and in the White Chalk, near Lewes (_Foss. South D._ tab.
xxiii. _fig._ 9).
[Illustration: Lign. 160. Shells of the family Ammonitidæ.
_Chalk and Greensand._]
Fig. 1.--Toxoceras Emericianum, and its septum. _Hamsey._
2.--Crioceras Puzosianum. (_M. D’Orbigny._) _Lewes._
3.--Ancyloceras furcatum, and its septum. _France._
In the genus Ancyloceras (_incurved horn_), _Lign. 160, fig. 3_, the
whorls are separate, and, at first, spiral (like _Crioceras_); but
afterwards the shell is prolonged, and then inflected at the large
extremity, like a Scaphite, but the whorls are not contiguous.
A very large species of _Ancyloceras_ occurs in the Kentish Rag, near
Maidstone, some specimens of which are eighteen inches in length. It
is figured and described, by the name of _Scaphites Hillsii_, in the
admirable Memoir of Dr. Fitton on the Strata below the Chalk (_Geol.
Trans._ vol. iv. pl. xv.); the present genus was not then established.
The Shanklin Sand in the Isle of Wight also contains a gigantic
species, which is figured and described by Mr. J. D. Sowerby, in the
_Geol. Trans._, as _Scaphites gigas_. _Ancyloceras_ occurs also in the
Oolite.
[Sidenote: TOXOCERAS. HAMITES.]
In Toxoceras (_bow-horn_), _Lign. 160, fig. 1_, the shell is slightly
curved, like a horn. Two or three species of _Toxoceras_ are found
at Hamsey. The tubercles, in the casts, are the bases of spines,
with which the back of the shell was armed, as I have ascertained
by examples examined in the rock (see _Foss. South D._ tab. xxiii.
_fig._ 1). The specimens figured of the above two genera occur in the
_Neocomian_ strata of France.
Hamites (_hook-shaped_). _Lign. 161, fig. 1._--Shell involute,
spiral, the turns not contiguous; spire irregular, elliptical; the
large end reflected towards the spire. The term _Hamite_, proposed by
the late Mr. Parkinson, was formerly given to all the fragments of
sub-cylindrical chambered shells, that were bent, or slightly hooked;
and the genera _Ancyloceras_, _Toxoceras_, &c., have been separated
from them, by M. D’Orbigny. But from fossils recently obtained from
Cretaceous strata in Pondicherry, and other parts of India, it seems
probable that these genera will be found to merge into each other; at
present it is convenient to keep up the distinction. The Hamites are
distinguished from Ancyloceras, which they most resemble, by their
elliptical, irregular spire.
Ptychoceras (_folded horn_). _Lign. 161, fig. 4._--This is another
genus formed from the Hamites. The shell is bent double in the shape
of a siphon, and the limbs are united together. The specimen figured is
from the _Neocomian_ strata of the Lower Alps.
[Illustration: Lign. 161. Hamites, etc. from the Chalk-marl.
Fig. 1.--Hamites cylindraceus, with part of the shell. (_M. D’Orbigny._)
2.--Baculites baculoides, with the mouth entire. _Hamsey._
3.--Part of the stem of the same species, showing the sinuous
septa. A detached septum is figured above.
4.--Ptychoceras Emericianum. (_M. D’Orbigny._)
]
[Sidenote: BACULITES.]
Baculites (_staff-like_). _Lign._ 161, figs._ 2 and 3.--This, as the
name implies, is a straight, elongated, conical, chambered shell; the
upper part is destitute of septa, and probably contained the body of
the animal.
In my early researches in the Chalk-marl of Hamsey, I discovered
numerous solid, oval, and cylindrical pipes of marl, with scarcely
any vestige of organic structure, whose origin it was impossible to
determine. At length I found the specimen, _Lign. 161, fig. 2_, which
showed the perfect aperture of a chambered shell; and afterwards I
found portions which displayed the foliated septa. (_Foss. South D._
tab. xxiii. _figs._ 5, 6, 7.) The Baculite, when perfect, is elongated
to a point; the septa are very numerous and foliated; the siphuncle
is situated on the margin. I have a splendid specimen from the Chalk
of France, (collected by _M. Alex. Brongniart_,) which is composed of
distinct casts of the cells, held together by the deep inflections of
their margins, in the same manner as are the sparry casts of Ammonites,
previously described.[421]
[421] See _Bd._ pl. xliv, _fig._ 5.
The Galt, near Folkstone, abounds in fossils of the above genera,
principally of _Hamites_; and the nacreous substance of the shells
is very often preserved. From the Chalk-marl near Dover, Southbourn,
Ringmer, and Southerham, near Lewes, and from Clayton, near
Hurstpierpoint, in Sussex, I have obtained examples of several species.
[Sidenote: SCAPHITES.]
Scaphites (_boat-like_). _Lign. 162._--This name was given by Mr.
Parkinson (_Org. Rem._ vol. iii. pl. x. See _Pict. Atlas_) to some
small chambered shells from the Chalk and Shanklin Sand, of a boat-like
form, with the inner whorls coiled up in a spire, and half hidden by
the outer chamber, which becomes contracted and recurved on itself,
is destitute of septa, and terminates in an oval or transverse mouth.
The siphuncle is dorsal. An _Ancyloceras_ closely coiled would be a
Scaphite. Hamsey marl-pit yielded to my early researches the first
Scaphites discovered in the British strata, together with Turrilites,
and other cephalopodous shells, previously unknown in England.[422] The
Scaphite is of an elliptical form, the spire and the mouth approaching
close to each other; the spire occupies about one-half of the shell.
Except the thick outer lip or margin of the aperture, which is almost
constantly found changed into pyrites, it is rarely that any vestige
of the shell remains. The same mineral constitutes casts of the spiral
part; and these, when separated from the other portion, might be taken
for Ammonites; see _fig._ 2. There are two varieties at Hamsey; one,
with the surface covered by fine transverse striæ, which arise singly
from the inner margins, and bifurcate on the dorsal part; _fig._ 1. The
other is also striated, but has a row of prominent ribs on the inner
half of the broad central portion of the shell; _fig._ 4. Scaphites
occur in the Upper Green Sand of Dorsetshire, and in the Chalk-marl
in several places in England; and at Rouen, in France; and a large
species, _S. Cuvieri_, has been found in New Jersey.
[422] Sow. Min. Conch, vol, i. p. 53.
[Illustration: Lign. 162. Scaphites. _Chalk-marl._ _Hamsey._]
Fig. 1 and 4.--Scaphites æqualis. (_Parkinson._)
2.--Cast in pyrites of the spiral part of a Scaphite.
2_a_.--Front view of the same specimen.
3.--Front view of Scaphites æqualis.
[Illustration: Lign. 163. Turrilites. _Chalk-marl._]
Fig. 1.--Turrilites catenatus. (_M. D’Orbigny._) _France._
_a._--One of the septa.
2.--Turrilites costatus. _Hamsey._
[Sidenote: TURRILITES.]
Turrilites. _Lign. 163._--Shell spiral, more or less conical, coiled
obliquely round an axis, and turriculated. Spire sinistral, whorls
contiguous, apparent, with a perforated umbilicus. Edges of septa
very sinuous. Siphuncle continuous, situated either on the external
convexity, or near the suture at the base of the wreath.
The discovery of three species of these elegant shells rewarded my
researches in the little marl-pit at Hamsey, already noticed, and
were the first examples of the genus found in England.[423] Like the
Ammonites, Scaphites, Hamites, &c. with which they are associated, the
Turrilites of our Chalk-marl seldom possess any traces of their shells.
The specimens are solid and tolerably sharp casts, with occasional
indications of the septa, and more rarely of the siphunculus. They
vary in size from two or three inches to two feet in length; and
are frequently more or less elliptical, from compression. The three
species which generally occur in the Sussex and Kentish chalk, are _T.
costatus_, _Lign. 163, fig. 2_; _T. tuberculatus_ (_Foss. South D._
pl. xxiv. _fig._ 7), characterised by its four rows of tubercles; and
_T. undulatus_ (_Foss. South D._ pl. xxiv. _fig._ 8), the wreaths of
which are ornamented with plain, slightly undulated, transverse ribs.
These are all reversed, or _sinistral_ shells; that is, the spire
is twisted to the left, the aperture being on the right hand of the
observer when the shell is placed on its apex, as in _fig._ 1. Several
other species of Turrilites occur in the Chalk of France,[424] one of
which, _T. catenatus_, is represented _Lign. 163, fig. 1_.
[423] Sow. Min. Conch, tab. xxxvi.
[424] See M. D’Orbigny’s Paléontologie Française.
Some of the Turrilites attain a considerable magnitude. The largest
found in England is a specimen of _T. tuberculatus_ (_Min. Conch._ tab.
lxxiv.), from Middleham, in the parish of Ringmer, near Lewes; when
perfect, it must have been full two feet in length: it consists of six
wreaths, the siphuncle, in the state of pyrites, appearing in three or
four; portions of the nacreous internal layer of the shell remain.[425]
In some specimens in my possession, the form of the aperture, and the
termination of the columella, are distinctly shown; as in the fine
example the last whorl of which is represented in _Lign. 164_.
[425] This specimen is now in the British Museum.
[Illustration: 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.
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.
[Sidenote: APTYCHUS.]
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 which is still somewhat problematical.
A good figure is given by Mr. Parkinson of one species (_Org. Rem._
vol. iii. pl. xiii. figs. 9, 10, 12. See _Pict. Atlas_), with the name
_Trigonellites latus_. These bodies frequently occur in pairs and in
apposition, as in the specimen figured in _Lign. 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 Chalk _Scaphites_ by 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 as _Trigonellites_, _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.
[Illustration: Lign. 165. Aptychus sublævis. 1/2 _nat._
_Kimmeridge Clay, Hartwell, Bucks._]
Fig. 1.--The convex surface.
1_a_.--Magnified section of portion.
2.--The concave side.
* * * * *
[Sidenote: 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 the study 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, the _Goniatites_. 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, the _Nautilus_ and _Spirula_ are 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._
_Existing Genera_
{ Argonauta. } Octopoda. }
{ Octopus, &c. } }
{ }
{ Loligo, Cranchia. }(_Teuthidæ_).} }
{ Sepiola, Onychoteuthis, &c. } } } Dibranchiata.
{ }Decapoda. }
{ Sepia (_Sepiadæ_). } }
{ } }
{ Spirula. } }
{
{ Nautilus (_Nautilidæ_). Tetrabranchiata.
_General fossil in the Tertiary Formations_
{ Sepiadæ { Sepia, Spirulirostra, Beloptera, Belemnosis.
{
{ Nautilidæ { Nautilus and Aturia
_Cretaceous Deposits_
{ Belemnitidæ { Belemnites, Belemnitella, and Conoteuthis.
{
{ Nautilidæ { Nautilus.
{
{ Ammonitidæ { Ammonites, Crioceras, Scaphites, Ancyloceras,
{ Toxoceras, Hamites. Ptychoceras, Helicoceras,
{ Turrilites, Baculites.
_Oolite and Lias_
{ Sepiadæ { Sepia.
{
{ Teuthidæ { Teudopsis, Beloteuthis, Geoteuthis, Leptoteuthis,
{ { Ommastrephes.
{
{ Belemnitidæ { Belemnites. Acanthoteuthis, and Belemnoteuthis.
{
{ Nautilidæ { Nautilus.
{
{ Ammonitidæ { Ammonites, Ancyloceras.
_Trias_
{ Nautilidæ { Nautilus.
{
{ Ammonitidæ[427] {Ammonites, Goniatites, and Ceratites.
_Carboniferous System_
{ Nautilidæ { Nautilus, Gyroceras, Cyrtoceras, Gomphoceras, and
{ { Orthoceras, Actinoceras, &c.
{
{ Ammonitidæ { Goniatites.
_Devonian System_
{ Nautilidæ { Nautilus, Clymenia, Cyrtoceras, Phragmoceras,
{ { Gomphoceras, Orthoceras, Actinoceras, &c.
{
{ Ammonitidæ { Goniatites.
_Upper and Lower Silurian Systems_
{ Nautilidæ { Nautilus, Lituites, Gyroceras, Cyrtoceras,
{ { Phragmoceras, Gomphoceras, Oncoceras, Ascoceras,
{ { Orthoceras, Actinoceras, &c.
X/
[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
sometimes _floats_, but _never sails_; and that the whole race of
Ammonites _died out_ in 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 broods
In 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."
* * * * *
[Sidenote: 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 often expose the inner cells, with the siphunculus,
in a beautiful state. The _Nautilus imperialis_ is 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 applying a 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
is _A. 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.
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 collecting _Belemnitidæ_, 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 and head, 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 (see _Lign. 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.
* * * * *
[Sidenote: 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 of
_A. 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 large _A.
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_, and _A. 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 of _A. biplex_, and _A. triplicate_.
In the Kimmeridge Clay in the vicinity, Ammonites with the shell
preserved.
Tisbury, Wilts. In Portland-stone, fine Ammonites, often chalcedonic
(see _Bd._ 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.
CHAPTER XIII.
FOSSIL ARTICULATA; COMPRISING THE ANNELIDES, CIRRIPEDES, CRUSTACEANS,
AND INSECTS.
The division of the Animal Kingdom termed _Articulata_, embraces, as
the name implies, those animals which have a _jointed_ body, generally
possessing an external-jointed skeleton, composed of segments more or
less annular and distinct. It comprehends six classes; namely--
1. Annelata, or Annelida; _i. e._ formed of rings; comprising the
Red-blooded Worms.
2. Myriapoda; as the Centipede.
3. Cirripedia; _i. e._ having curled-feet; as the _Balanus_ and _Lepas_
(Barnacle).
4. Crustacea; as the Crab, Lobster, and Water Flea.
5. Arachnida; Mites, Scorpions, and Spiders.
6. Insecta, or Insects.
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 of _Articulata_, 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 (the _Dorsibranchiata_ and _Abranchiata_), and move with great
celerity; as the _Gordius_, or Hair-worm, and the _Nereis_, so frequent
on the sands of the sea-shore. Others have shelly coverings (the
_Tubicolæ_), as the _Serpula_, 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 the _Sabella_ (_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.
[Illustration: Lign. 166. Fossil impression of Nereis. _Silurian
strata._
(_Drawn by Miss Murray._)
Nereites Cambrensis. (_Murch. Sil. Syst._) _Llampeter._]
[Sidenote: 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 of Nereis (_Dorsibranchiate_) are free, 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 in _Lign. 166_ indicates 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 the _cirri_ of 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 the _Gordius_, 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.
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 the _Serpulæ_ are
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 tortuous
_Serpula_ is 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 of
_Serpulidæ_, 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 composed of 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 or _Barnacles_ are divided into two groups;
namely, the _sessile_, or those which in their adult state are fixed by
the base to other bodies, (Balanidæ,) as the Acorn-shell, or _Balanus_;
and the _pedunculated_, which have a process of attachment, peduncle
or stem, (Lepadidæ,) as the Duck-barnacle, or _Lepas_. 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 the _Cirripedes_
have been generally figured and described in works on Conchology as
being allied to the _Mollusca_.
[433] See Mr. C. Darwin’s admirable Monograph on the Cirripedia,
published by the Ray Society, 1851.
Balanus. _Lign. 167, fig. 1.3_--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 called
_parietal_ valves; and of pieces termed _opercular_ valves, by which
the aperture is closed. The shell of the _Balanus_, 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. The
fossil _Balanus_, _Lign. 167. fig. 1_, is from the Crag, 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 newer _Pliocene_
deposits of the Sub-Apennines, and of North America, several species
are common.
[Illustration: 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_) of Scalpellum 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 by _Pholades_.
(_Mr. Bensted._) _Lower Green Sand._ _Maidstone._
_a._ The _Nerites_ lodged in the cavities.
_b._ Fragment of wood remaining attached.
]
[434] Figs. 5 and 6 are referred to and described at pages 409 and 410,
vol. i.
Lepadidæ.--The pedunculated Cirripedes, of which the common
_Duck-barnacle_ is a well-known example, have a strong, muscular,
hollow stalk, or peduncle, which supports a multivalve shell,
containing the body of the animal. In _Pollicipes_ and _Scalpellum_
there 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 Tertiary _Scalpellum quadratum_ is sometimes better preserved;
and Mr. Morris has described a most beautiful group of _Pollicipes_
(_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 Fossil _Lepadidæ_,
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 distinct _branchiæ_, 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, diffused more 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 or _cephalic_, the _thoracic_, and the _abdominal_;
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. The _thoracic_ portion 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 (called
_Edriopthalmia_), 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 is very 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 this _phrenological method_
to the investigation of the fossil crustaceans.
[437] Histoire Naturelle des Crustacés Fossiles; par MM. Alex.
Brongniart et Desmarest. 1 tom. 4to. Paris, 1822.
The fossil remains of Crustaceans consist of the calcareous covering
or carapace, with the articulated extremities, and, rarely, the
jaws and antennæ. For the most part, the specimens are mutilated,
and present only portions of the carapace, abdominal segments, and
detached claws; but in strata composed of very fine detritus, such as
the cream-coloured limestones of Solenhofen and Pappenheim, examples
often occur in the most beautiful state of preservation, appearing as
if the animals had been carefully embalmed in a soft paste, that had
quickly consolidated around them, and preserved them without mutilation
or blemish. In some examples, even the colour of the original remains.
The specimens found in hard limestones and coarse conglomerates are
generally mutilated, and, as the under surface of the carapace, and
the sternal plates to which the legs are attached, present more
irregularity than the dorsal portion of the shell, they are firmly
impacted in the stone, so as to render the development of some of the
most important characters difficult, if not impossible. The antennæ
and claws are often separated, or altogether wanting; the most common
relics being the pincers and the carapace, or united cephalo-thoracic
segments. The substance of the shell, which in the recent state
consists of phosphate and carbonate of lime, with gelatine or
cartilage, is commonly a friable carbonate of lime, tinged with oxide
of iron. These remarks apply more particularly to the crabs, lobsters,
shrimps, prawns, &c. Numerous species of the smaller crustaceans, as
the_ Cypris_, and the extinct family of _Trilobites_, occur in myriads,
and, in some formations, are the principal constituent of deposits of
great thickness and extent.
The remains of this class have been found throughout the vast series of
the fossiliferous strata. Extinct forms appear in prodigious numbers in
the most ancient formations, and are succeeded by genera which approach
more nearly to the more highly organized crustaceans. The Crab and
Lobster tribes are represented by certain species in the Lias, Oolite,
and Chalk; while in many of the Tertiary strata the existing types
prevail.
The London Clay, in the Isle of Sheppey, yields many beautiful examples
of the higher order of crustaceans, as the Crab, Lobster, &c. In the
Chalk these remains are more rare, but a few fine specimens have been
obtained. On the Continent, certain localities are extremely rich
in these remains. Upwards of sixty species were discovered by Count
Münster in the Jura limestone, at Solenhofen; and the Muschelkalk
of Germany has yielded several extinct genera. The beautiful state
in which these fossils occur, is exemplified in the specimen from
Solenhofen, figured in the frontispiece of this work; _Pl. I. fig. 2_.
Fossil Crabs.--Of the _brachyurous_, or short-tailed, crustaceans,
of which the common Crab is an example, and of the _Anomura_
(abnormal-tailed), there are remains of several genera in the Tertiary
deposits. The Isle of Sheppey is the most productive locality in
England. The carapaces of several kinds occur in the septaria and
nodules of indurated clay; the chelate hand-claws (_pincer-claws_)
are often found detached, and sometimes in connexion with the shield.
The most numerous specimens are referable to two species. One of them
(_Cancer Leachii_) is from two to three inches wide, and has a convex
shell, the surface of which is covered by minute punctations, with
three tubercles on each anterior lateral margin.[438] The carapace of
the other species is more distinctly lobed, and studded with aculeated
or spiny tubercles; it is named _C. tuberculatus_.[439]
[438] Hist. Nat. Crust. Foss. pl. viii. figs. 5 and 6.
[439] König, Icones Foss. Sect. _fig._ 54. These two species are now
referred to the genus _Zanthopsis_.
A species of Crab, characterised by its relatively large claws, is
common in the soft Tertiary limestone of Malta; and examples, in a fine
state of preservation, are often seen in cabinets; see _Wond._ p. 251.
I am not aware that vestiges of more than one genus of brachyurous
crustaceans have been observed in the British Secondary formations;
namely, the _Podopilumnus Fittoni_ (M‘Coy), from the Greensand of Lyme
Regis: but several small species belonging to the anomurous group have
been found in the Galt.
In the _Galt_ at Ringmer, a village near Lewes, I discovered, many
years since, four or five species of small crustaceans, which are
figured and described, _Foss. South D._ pl. xxiv.; their natural
relations were pointed out to me by the late eminent naturalist, Dr.
Leach. Specimens of two of the species have since been collected at
Folkstone, but as these are only the carapaces, no additional light has
been thrown upon the structure of the originals.
The smallest species consists of the carapace or cephalo-thoracic
segments, united into a transversely obovate, obscurely trilobate
shell, the surface of which is covered with minute irregular papillæ;
with four tubercles on each lateral portion, and an irregularly
tuberculated dorsal ridge (see _Lign. 168, fig. 1, 1a._); it
probably belongs to the genus Etyus; and I have named it _Etyus
Martini_, in honour of my friend, P. J. Martin, Esq., author of several
excellent Memoirs on the Geology of Western Sussex.
[Illustration: Lign. 168. Fossil Crustaceans: _nat._ _Galt._ _Near
Lewes._