Chapter VII (2)

It may here be necessary to notice a prevailing error, regarding the mode in which the substance called coral is produced. It is very generally supposed that Corals, particularly those bearing stars and cells, have been constructed by animalcules, in the same manner as is the honey-comb, by the Bee; and the expressions often employed by naturalists, of "the coral animalcules building up their rocky habitations," and "constructing their cells," have contributed to foster this error. But the processes are in no respect similar: the insect, under the guidance of an unerring instinct, resulting from its peculiar organization, _constructs_ its cells; but the polype is incapable of forming, or even modifying, its support or cell in the slightest degree. The polypidom is _secreted_ by the animal tissues, in the same manner as are the bones in the vertebrated animals, without the individual being conscious of the process. If a piece of white coral be immersed in dilute hydrochloric acid, the calcareous part is dissolved, and the secreting membrane, in the form of a flocculent substance, is seen attached to the undissolved part; even in some coralline marbles of incalculable antiquity, the animal membrane may, in this manner, be detected.[231]

[231] See Pict. Atlas, pl. xxxiv. _fig._ 2.

From the delicate and perishable nature of many of the gelatinous zoophytes, numerous tribes may have inhabited the seas, which deposited the fossiliferous strata, and yet no indications of their existence remain; while, of others, but obscure traces of their structure are likely to be detected.

The Polypifera are separated into two natural groups or classes; viz. the Anthozoa (flower-animals), and the Bryozoa (moss-animals), or Polyzoa.

The Anthozoa are polypes of the most simple type of structure. The body consists of a symmetrical gelatinous sac, capable of contraction and expansion, with one aperture or mouth, which is encircled by tentacula. The Hydra, or fresh-water polype (_Wond._ p. 600), is a familiar example of a single, locomotive, anthozoan animal. In the compound or aggregated forms, the body is either inclosed in a horny sheath (ex. _Sertularia_, _Wond._ p. 615), or is supported by a lamellated calcareous endo-skeleton (ex. _Fungia_, _Wond._ p. 623, pl. vi. _fig._ 15), or the soft parts invest a stony axis (ex. _Madrepora_, _Wond._ p. 620), or a horny flexible framework (ex. _Gorgonia_, _Wond._ p. 616).

The Anthozoa are subdivided into three orders, which are based on the peculiar characters of the polypes; the _Hydra_, the _Actinia_ (Sea-Anemone, _Wond._ p. 622), and the _Alcyonium_ (Dead-men's fingers, _Wond._ pl. v. _fig._ 10), being respectively the type of 1. the _Hydroida_, or Hydraform; 2. the _Asteroida_ or Alcyonian; and 3. the _Helianthoida_, or Actiniform zoophytes.

In the Hydroida the body in the compound species is implanted in a horny tubular sheath, and the polypidoms form branched corallines, which are fixed by the base to rocks, sea-weeds, shells, &c.

The Asteroida have a horny or calcareous axis, surrounded and inclosed by the soft parts which secrete it.

The Helianthoids, except in the simple free species, as the Actinia, have a lamellated calcareous polypidom, the plates of which radiate from a centre.

The calcareous secretions of the Anthozoa, especially of the Helianthoida, in a great measure constitute the mass of the coral-reefs and coral-islands of tropical seas. Their polypidoms, whether external or internal, maintain but little organic connexion with the compound soft substance. These zoophytes increase by gemmation or budding; some throw up germs from the disk, as in Astreadæ; others laterally, as in Caryophillidæ; and some spirally along the stem, as in Madreporidæ; examples of these modes of reproduction are often found in fossil corals. The increase of coral-rocks is produced by the continual formation of new masses, by the successive generations which spring up as it were from the bodies of their parents; layer upon layer, and tier upon tier, of Helianthoid polypidoms, are found to compose many of the coralline limestones of the palæozoic formations.

Fossil Anthozoa.--The first group of extinct corals to be noticed under this head is the _Graptolitidæ_, a family restricted to the Silurian rocks, and whose natural affinities have been much questioned; some palæontologists referring them to the _Pennatulidæ_, or Sea-pens, others to the _Sertulariadæ_.[232]

[232] For a full consideration of this subject, refer to Prof. McCoy's Brit. Palæozoic Fossils.

[Sidenote: GRAPTOLITES.]

(_Murch. Sil. Syst._)

Fig. 1.--Graptolites ludensis.[233]
1_a_.--Magnified view of a portion of the same.
2.--Graptolites Murchisoni.
2_a_.--Magnified portion of _fig._ 2.
]

[233] _Ludensis_, from Ludlow--to indicate the habitat of the fossils.

Graptolites. _Lign. 85._--These curious zoophytes abound in many of the Silurian deposits; they consist of sessile polype cells, arranged in one or two rows to a flexible stem, like the recent Sertularia, or Virgularia. Prof. McCoy refers them to the order Hydroida.

In a recent state these bodies were probably covered with a soft, or albuminous mass, studded with polype-cells, disposed in rows along the margins of the lateral, curved, grapple-like processes, as in the zoophytes termed _Virgularia_,[234] to which one kind bears a great analogy. If two specimens of the _Graptolites Ludensis_ be placed together, so that the elongated smooth edges be in apposition, the united stems will be seen to offer a general resemblance to the axis of _Virgularia mirabilis_.

[234] See British Zoophytes, pl. xxiv.

M. Barrande divides the Graptolites into three groups or genera, which are defined as follow:--

_Graptolites_ (proper), a single series of cells united together at the base, and adhering along the sides nearly to the orifice of each cell, as in _fig. 1a_. _Monoprion_ of M. Barrande.

_Rastrites._--The axis reduced to a mere line, on which the cells are placed at relatively wide intervals, and but slightly inclined. These two genera are supposed to have been hydroid zoophytes, and related to the Sertularidæ.

_Diprion_ (_Diplograpsus_ of Mr. McCoy), cells in two series arranged along a central axis; these forms present a foliaceous appearance; they are presumed to resemble the existing genera Pennatula and Virgularia.

Graptolites have been found in strata of the same age in Norway, Sweden, and Scotland.[235] I have received slates literally covered with them, from the Silurian rocks of the United States, by the kindness of my friend, Benjamin Silliman, jun. Esq.

[235] Many species of Graptolites from the Lower Silurian rocks of the South of Scotland, are described and figured by Mr. Harkness in Geol. Journal for 1850, vol. vii. p. 58, pl. 1.

Sir R. Murchison remarks, that the nature of the strata in which these remains occur in Radnorshire, indicates a condition of the sea, well suited to the habits of the family of Pennatulidæ, or Sea-pens; for the recent species live in mud and slimy sediment, and the fossils are imbedded in a finely levigated _mud-stone_, which, from its structure, must have been tranquilly deposited.

* * * * *

I will next describe the single lamellated Anthozoa, and afterwards notice those corals which consist of an aggregation of radiated cells, either frondescent, or disposed in solid masses.

[Sidenote: FUNGIA. ANTHOPHYLLUM.]

Fungia (_Wond._ p. 623).--The corals thus named, from their supposed resemblance to fungi, are of a depressed form, and have the under surface scabrous; they are divided above by numerous lamellæ, or plates, which radiate from a central, oblong depression.

When living, the solid stony polyparium is enclosed in the gelatinous mass by which it was secreted, and there are numerous tentacula around the central cavity, or sac. These zoophytes may be compared to the _Actiniæ_, or Sea-Anemones, from which they differ only in having a calcareous axis, while the Actiniæ have a tough albuminous integument. (_Wond._ pl. vi. _fig._ 15, represents the living animal; and _Lign. 141, fig. 2_, p. 641, and _Lign. 58, fig. 4_, two fossil species).[236]

[236]

Fungia numismalis. Pict, Atlas, pl. xxxvi. _fig._ 6.
------ polymorpha. Ibid. pl. xliii. _fig._ 1--4; pl. xlv, _fig._ 11.

Anthophyllum Atlanticum. _Lign. 88. fig. 4._--In the arenaceous strata of the United States, which the researches of Dr. Morton, of Philadelphia, have proved to be the equivalents of the European Cretaceous formation, a single lamellated coral is not uncommon. It is evidently related to the Fungiæ, and has been named as above by Dr. Morton.

Turbinolia Königi (_Wond._ p. 320).--Polyparium turbinated, striated externally, detached, base not adhering; cell single, radiated.

This genus occurs in all the fossiliferous deposits: a small, well-marked species is frequently met with in the Galt, of which subdivision of the cretaceous strata it is a characteristic fossil. It is figured _Wond._ _Lign. 58, figs. 1, 2_.[237]

[237]

Turbinolia complanata. Ibid. pl. xxxvi. _fig._ 9.
---------- mitrata. Ibid. pl. xxxvi. _fig._ 10.

Caryophyllia centralis (_Lign. 89 figs. 1, 2_: _Lign. 88, fig. 5_).--Polyparium turbinated, or cylindrical, simple or branched, longitudinally striated, fixed by the base; cells lamellated.[238]

[238] Monocarya (of Lonsdale), Dixon's Fossils, p, 244.

A small recent species (_C. cyathus_), is very common in the Mediterranean, and frequently seen in collections: it is cyathiform, and the base by which it is attached to other bodies, is broad and spreading; the newer tertiary deposits of Sicily contain this species in abundance.

A Caryophyllia, bearing a general resemblance to this species, is common in the chalk, and occurs in beautiful preservation (_Wond._ _Lign._ 58, _fig._ 3).[239]

[239]

C. centralis, Pict. Atlas, pl. xxxvi. figs. 15, 16.
C. annularis, ibid. pl. xxxvii. _fig._ 5.

Branched Caryophylliæ are found in the Coralline Oolite and Dudley Limestones (_Sil. Syst._ pl. xvi.). A large proportion of the Coral-rag of the Middle Oolite is composed of a branched species (_C. annularis_) of this genus; _Lign. 88, fig. 5_, represents a specimen from near Faringdon.

_Devonian limestone. Eifel._

Fig. 1.--Portion of a branch of the coral; _nat._

2.--Fragment, slightly magnified, with part of the surface broken
away below, exposing the central axis, and radiated
arrangement of the cells, with their lateral pores.

3.--Another portion, magnified, showing the polype-cells hollow.
]

Favosites polymorpha. _Lign. 86. Lign. 88, fig. 3._--Polyparium stony, polymorphous, solid internally, compact, composed of a congeries of diverging or ascending parallel, contiguous, prismatic tubes, covered by pores, divided by lamellæ, and communicating by lateral foramina.

The corals of this extinct genus abounded in the Silurian and Devonian seas; the remains occur with those of other fossil zoophytes of that epoch in great numbers, both in Europe and North America. I have many beautiful examples from the Silurian rocks of the Ohio and Niagara, by favour of Dr. Owen, of New Harmony, and Dr. Yandell, of Louisville, in which the cells are filled up with calcareous spar. The varied markings on many of the Babbicombe marbles, and Torquay pebbles, are derived from the enclosed Favosites (_Wond._ p. 643).

Another species (_Favosites Gothlandica_) occurs in masses of a subconical shape, and is common in some of the Silurian limestones. A fragment, to show the structure, is figured _Lign. 88, fig. 3_.

[Sidenote: CATENIPORA. SYRINGOPORA.]

Catenipora (_Wond._ p. 644, _fig._ 3).--Polyparium hemispherical, composed of vertical anastomosing lamellæ; cells tubular, oval, terminal, united laterally. The oval form of the cells when united laterally, and the flexuous disposition of the lamellæ, give rise in transverse sections to elegant catenated markings, from which appearance the fossil has received the name of _chain-coral_.[240] The species figured (_C. escharoides_) in _Wond._ is common in the Silurian limestones, and sometimes forms hemispherical masses more than a foot in diameter. The chain-coral is extensively distributed through the Silurian rocks of the United States. Coloured figures of this exquisitely beautiful coral are given in _Pict. Atlas_, pl. XXXV.

[240] Org. Rem. vol. ii. pl. iii. figs. 4, 5, 6.

Syringopora ramulosa. _Lign. 88, fig. 2._ (_Wond._ p. 641.) These corals bear a general resemblance to the Organ-pipe Coral of Australia. The polypidom is composed of long, cylindrical, vertical tubes, distant from each other, and connected by transverse tubular processes; the cells are deep and radiated by numerous lamellæ.

The external aspect of these fossils is that of a cluster of cylindrical pipes, more or less parallel, connected by short transverse branches. They are the _Tubiporites_ of Mr. Parkinson, who has given admirable figures of several specimens.[241] In these fossil corals that excellent observer first detected the animal membrane. A slab of marble, whose markings are produced by the section of the inclosed tubes of a Syringopora, is represented, _Wond._ p. 644, _fig._ 2. The Mountain limestones of Derbyshire, and of Clifton, on the banks of the Avon, contain figured marbles of this kind, which are manufactured into vases, tables, &c. The genus is extinct.

[241] Pict. Atlas, pl. xxxv. _fig._ 1. Syringopora geniculata, Pict. Atlas, pl. xxxiv.

Lithostrotion Columnaria (_Wond._ p. 641, _fig._ 8).--Polyparium massive, solid, composed of aggregated, contiguous, parallel, prismatic tubes, each terminated by a star: cells shallow, multi-radiate, stelliform.

Species of this extinct genus are common in the mountain limestone, in large masses, which, from the pentagonal form, and parallel arrangement of the tubes, appear like clusters of miniature basaltic columns.[242]

[242] Lithostrotion striatum, Pict. Atlas, pl. xxxvii. figs. 5, 6.

[Sidenote: CYATHOPHYLLUM.]

Cyathophyllum. _Lign. 87, figs. 1, 2._ (_Wond._ p. 641, _figs._ 1, 3.)--Polyparium turbinated, simple or compound, internal structure transversely chambered or lamellated; cells polygonal, radiated, depressed in the centre.

The corals of this genus are so abundant in the Silurian rocks, that the seas of that epoch must have swarmed with them. The simple turbinated forms are often several inches long, and being somewhat curved, have obtained the popular name of "_petrified rams-horns_."

Upon slitting one of these corals vertically, as in _Lign. 87, fig. 1_, the axis of the polyparium, beneath the cell, is found to consist of thin transverse partitions, constituting a series of chambers.

In the compound Cyathophylla, the germs of young cells, occupying the disc of a parent cell, are often met with. _Fig._ 3 represents a group of four germs on the parent cell, of _C. dianthus_, a common and beautiful coral of the Dudley limestone.

(_Sil. Syst._)

Fig. 1.--Cyathophyllum turbinatum: an oblique longitudinal section,
showing at a the transverse lamellæ, or cells, of the internal
structure.
2.--The same species.
3.--Cyathophyllum dianthus: a Specimen, with four young germs
arising from the disc below.
4.--The same species, with four adult cells.
]

These corals are also prevalent in South Devonshire, and many of the elegant marbles of Babbicombe are figured by the sections of these polyparia.[243]

[243]

Cyathophyllum turbinatum, Pict. Atlas, pl. xxxvi.
------------- fungites, ibid. pl. xxxviii.

Associated with the Cyathophylla in the Silurian rocks, are certain corals that attain considerable magnitude, and which are principally distinguishable by their internal structure. Such are _Cystiphyllum_, constructed of bladder-like cells, and _Strombodes_, composed of spirally contorted lamellæ, or plates (_Sil. Syst._ pl. 16^(bis), _fig._ 4). Other hemispherical masses, presenting on the surface concentric wrinkles, with very minute pores, are common at Dudley, and belong to the genus _Stromatopora_.

_Upper Silurian, Dudley._[244]

Fig. 1.--Astrea ananas.

1_a_.--A polished slice of Marble, formed of Astrea pentagona.
_Devonian. Torquay._

2.--Syringopora ramulosa. _Mt. L. Derbyshire._

3.--A Fragment of Favosites Gothlandica. _Ohio._ (_By Dr. Owen._)

4.--Anthophyllum Atlanticum. _Cret. U. States._ (_By Dr. Morton._)

5.--Caryophyllia annularis. _Oolite. Faringdon._
]

[244] Figured in Pict. Atlas, pl. xxxvii. _fig._ 1.

[Sidenote: ASTREA.]

Astrea. _Lign. 88, figs. 1, 1a._--Polyparium massive, irregular in shape, generally globular, formed by an aggregation of lamellated, radiated, shallow, polymorphous cells.

The corals of this genus are very numerous in the seas of the Tropics, and there are many species in the Oolite, and older secondary formations. The Astreæ, Caryophylliæ, Cyathophylla, &c., form the principal mass of the coralline limestones of the Oolite, termed the _Coral-rag_, from the abundance of these relics: being literally composed of an aggregation of large corals, the interstices of which are filled with shells, radiaria, &c., either whole, or in a comminuted state. The heaps of this limestone placed by the road-side, in the N. W. of Berkshire, appear like fragments of an old coral-reef, and attract the notice even of the most incurious observer. I have figured a specimen of Astrea, _Lign. 88, fig. 1_, and a polished section, _fig. 1a_, from Clifton, a locality well known for the stupendous mural precipices of mountain limestone rocks, which yield beautiful examples of coralline marble.[245] The mode of increase of the Astrea is very curious; a subdivision takes place in the old cells, after the manner of the Infusoria; and among the fossils, a star or cell may often be seen in progress of division into two, three, or four stars (_Sil. Syst._ pl. xvi. _fig._ 6). A living polype of this genus is figured, _Wond._ pl. vi. _fig._ 13.

[245]

Astrea arachnoides, Pict. Atlas, pl. xxxviii. _fig._ 4.
------ undulata, ibid, pl. xxxviii. _fig._ 10.
------ Tisburiensis ibid. pl. xxxviii. figs. 12, 13.

A species of Astrea (_A. Tisburiensis._ _Wond._ p. 641, _fig._ 9), is found in large hemispherical masses, completely silicified, at Tisbury, in Wiltshire. The transverse surface displays, in some specimens, beautiful white radiated stars, on a dark blue ground; and in others, the colours of the stars and ground are reversed. This silicified coral is obtained from a bed of chert, a foot in thickness, which is interstratified with the Portland limestone, this division of the Oolite being quarried around Tisbury.[246]

[246] See Catalogue of the Organic Remains of Wiltshire, p. iv. by Miss Etheldred Benett. 4to. 1831.

In the tertiary clays at Bracklesham Bay, Sussex, a beautiful small coral of this type (_Siderastrea Websteri_, Dixon's Foss. tab. i, 5), is found attached to flint pebbles.

Several species of this and the following genus, perfectly silicified, are found in the state of pebbles and boulders in the superficial soil of Antigua, and other islands of the West Indies, associated with the fossil palms, described in a former part of this work. Some of these corals are of great beauty, and polished sections exhibit the coralline structure most perfectly.[247]

[247] In the "Spongitenkalk," at Nattheim, near Heidenheim, all the corals are replaced by chalcedony.

Madrepora.--Polyparium arborescent or frondescent, porous, fixed; cells deep, with twelve rays, prominent, irregularly dispersed on the surface, and accumulated towards the terminations of the coral.

The term madreporite, or fossil madrepore, was formerly applied to all the branched fossil corals with radiated cells, but is now restricted to those which possess the above characters. The recent common species, figured _Wond._ p. 620, will serve to illustrate this genus. The elevated, branched Madrepores, with minute polygonal cells having twelve rays, the lamellæ of which are denticulated, are termed Porites, and are frequent in the Silurian strata (_Sil. Syst._).

Millepora. _Lign. 89._--Coral ramose; cells very minute, distinct, perpendicular to the surface, giving the interior a finely striated fracture, disposed irregularly.

There are many fossil species of this genus, some of which are of considerable size. A small species from the mountain limestone is figured _Lign. 89, fig. 7_.[248]

[248] Millepora, Pict. Atlas, pl. xl. _fig._ 6.

Lithodendron. _Lign. 70, fig. 3._--Polyparium branched, formed of deep, cylindrical, elongated cells, which are terminal, and radiated, with a prominent central axis.

Large masses of corals of this genus, composed of clusters of branches, are imbedded in the mountain limestone of Derbyshire, Yorkshire, &c.; and a few species occur in the Coralline Oolite; their general configuration will be understood by the figure _Lign. 70, fig. 3_; but in this specimen the margins of the cells are worn off, and do not present the original deeply excavated form.[249]

[249] Lithodendron fasciculatum, Pict. Atlas, pl. xxxviii.

There is a remarkable specimen of this coral in the Bristol Institution (of which a portion is now placed in the Museum of Practical Geology, in London), that was discovered by Mr. Samuel Stutchbury,[250] in a vein of hematitic iron ore. It is a large mass, in which the entire substance of the coral is transmuted into a metallic ore, forming one of the most interesting natural electrotypes I have ever seen. In this instance, a block of Lithodendron must have lain in a vein or fissure of the rock, and its animal membrane have resisted the action of the gaseous emanations, or mineral solutions, while the calcareous polypidom was dissolved, and the metallic matter deposited atom by atom, as in the case of pseudo-morphous crystals.

[250] Now of Sydney, Australia.

Gorgonia.--Of the flexible anthozoan coral, which from the flabellated form of the polyparium is generally called "Venus's fan," and by naturalists _Gorgonia_, a few fossil species have been discovered and determined. From the friable arenaceous limestone beds of Maestricht, which abound in corals, fine specimens of a delicate species are occasionally procured. _Wond._ p. 320, _fig._ 5, shows the character of this fossil zoophyte.

Fossil Bryozoa.

[Sidenote: FOSSIL BRYOZOA.]

The second class of Polypifera, the Bryozoa or _Polyzoa_, are of a much higher order of organization than those which have engaged our attention. The body is not symmetrical, nor capable of contraction and expansion, as in the Anthozoa: it consists of a digestive cavity or sac, which is bent on itself and open at both extremities. The outer integument is either membranaceous or horny; sometimes calcareous. The oral aperture or mouth is surrounded by a circle of tentacula, from eight to twelve or more in number, and these tentacles are clothed with vibratile cilia. (_Wond._ p. 606, the polype of _Flustra pilosa_.)

The polypes in this order never occur singly; they are always united by a common integument, but each enjoys an individual existence. The animal can extend its tentacula and protrude the mouth from the cell, but the rest of the body is incapable of extension or contraction. These polypifera increase by germination. In their organization, they so closely approach the mollusca, that in recent zoological systems they are placed in that class. The ciliated character of their tentacula has also led to their being named _Cilio-branchiata_. But as it is desirable in a work of this elementary nature to avoid conflicting opinions as much as possible, the fossil Bryozoa will be considered as corals, in the general sense of that term.

[Sidenote: FLUSTRA. ESCHARA.]

Flustra (_Sea-mat_). _Lign. 89, fig. 4, 5._--The polyparium is either membranaceous and flexible, calcareous and encrusting, or foliaceous, composed of cells, arranged in juxtaposition, more or less quadrangular, flat, with a distinct border, disposed on a flat surface, or on opposite surfaces, as in the _F. foliacea_.

This is one of the most common genera of the encrusting and frondescent zoophytes. The _Flustra_ consists of a cluster, or aggregation of polypes, invisible to the naked eye; under the microscope, the polype is found to be a transparent gelatinous body bent on itself, with a sac or digestive cavity, having two apertures, the external margin of which terminates in eight or ten tentacula, clothed with cilia; the whole is surrounded by a firm wall, constituting a cell, from which the animal can protrude its tentacula and upper part. (Figures of the living polypes of Flustræ, _Wond._ p. 605, _pl._ vi. _fig._ 6, 7.)

Many species of _Flustræ_ occur in the British strata: the encrusting forms are attached to echinites, shells, &c.; the foliaceous are imbedded in chalk, sand, sandstone, &c. In Mr. Morris's _Cat. Brit. Foss._ ten species are enumerated; none of these are from formations below the Chalk. I have selected for illustration a Flustra attached to an echinite from Lewes. _Lign. 89, fig. 5_, represents a small portion of the natural size; and _fig. 4_, a few cells magnified, to show their form and arrangement. A foliaceous zoophyte, apparently a bryozoon, is abundant in the Sussex and Kentish chalk, and is often disposed in angular folds. It is generally of a ferruginous colour, and, from its friable texture, it is probable the original consisted of a membranous polypidom or calcareous substance; specimens sometimes extend over several square inches of the chalk. It is common in the chalk-pit at Off ham, near Lewes.[251]

[251] In my South Down Fossils, pl. xv. _fig._ 6, a specimen of this kind is described as a Ventriculite, _V. quadrangularis_. An admirable lignograph of a remarkable example is given by Mr. Toulmin Smith, under the name of _Brachiolites angularis_; it presents ten deep, flat, angular folds, and has radicle and lateral processes; see "On the Ventriculidæ," p. 93.

Eschara.[252]--In these zoophytes the polyparium is encrusting or foliaceous, calcareous and brittle; the cells are thickened on their outer margins, and have a small, depressed, round aperture. They are arranged in two series of planes, adhering together, the cells on each surface exactly corresponding.

[252] So named from a supposed resemblance to an eschar.

Species of Escharæ are found either in flints, or attached to echinites, and other bodies; they have the appearance of patches of flustræ, but with a lens may be distinguished by the symmetrical juxtaposition of the cells on the opposite sides of the polyparium.

Lign. 89. Corals from the Chalk and Mountain Limestone.

Fig. 1.--Carophyllia centralis; _nat._ (G. A. M.) _Cret. Lewes._

2.--Front view of half the disc of the same.

3.--Two cells of Crisia Johnstoniana. × ×.

4.--Magnified view of six cells of the Flustra, _fig._ 5.

5.--A portion of an encrusting Flustra; _nat._ _Cret. Chichester._

6.--Idmonea (Dixoniana) cretacea; _nat._ _Cret. Lewes._
The figure on the left shows the under surface; that on the
right, the upper surface, with a row of polype-cells on
each margin: a portion magnified is given _fig._ 12.

7.--Millepora rhombifera. × ×. _Mt. L. Ph. Yorks._
The small figure on the left is of the natural size.

8.--Pustulopora pustulosa. × ×. _Cret. Chichester._
The small figure on the left, _nat._

9.--Homœsolen ramulosus. × ×. _Cret. Dover._
The left-hand figure, _nat._

10.--Crisia (?) Johnstoniana. (G. A. M.) × 250 linear.
_S. s. Maidstone._

10_b_.--Two cells of the coral, _fig._ 10, seen in profile, × ×.

11.--Homœsolen ramulosus; _nat._ _Cret. Lewes._

12.--Idmonea Dixoniana; a portion of _fig._ 6. ×.

13.--Retepora laxa. _Mt. L. Ph. Yorks._

13†.--A portion of the same ×.

14.--Idmonea Comptoniana. × ×. (G. A. M.) _Chalk, Chichester._
(_Mr. Walter Mantell._)
The small figure on the right is of the natural size.
]

[Sidenote: MICROSCOPIC FOSSIL BRYOZOA.]

Crisia Johnstoniana. _Lign. 89, fig. 3, 10, 10b._--The minute recent corals thus designated are allied to _Flustra_, but separated from that genus by the cells being disposed in a single series, and united by connecting tubes. I notice this genus to direct attention to a very curious polypidom from the Greensand of Maidstone, presented to me by Mr. Bensted. The specimen is attached to a fragment of shell. The cells, five of which are represented, _fig._ 10, are elliptical, with the aperture above, and towards one extremity; they are united by very slender, hollow filaments: _fig. 3_, two of the cells seen from above × 250 linear; _fig. 10b_ the same seen in profile.[253] I have named this species _C. Johnstoniana_, as a tribute of respect to the author of the admirable works on British Zoophytes, previously noticed.

[253] I refer this fossil to the genus _Crisia_ with some hesitation; perhaps _Hippathoea_ would be more correct, but all the described species of the latter are branched.

The fragmentary relics of numerous minute and elegant corals, constitute a considerable portion of the mass of some of the white chalk strata; several genera of these zoophytes are figured in Mr. Dixon's beautiful work, and described by Mr. Lonsdale. Attached to the surface of shells, &c., and sometimes standing erect in little crannies, or hollows, of the flints, many beautiful corals may often be detected with the aid of a lens. By brushing chalk in cold water, and examining the deposit, the student will probably discover several of the species figured in _Lign. 89_, which we proceed to describe.

Retepora (_Lace-Coral_). _Lign. 89, fig. 13._--A very thin calcareous polyparium, disposed like net-work in foliaceous and branching plates; cells opening either on the upper or inner side.

These are an elegant tribe of corals, of which many species occur in the Chalk formation at Maestricht, in the white-chalk of England, in the mountain limestone of Yorkshire, (_Phil. York._), and in the Silurian deposits (_Sil. Syst._). It may be useful to state, that in the description of the fossil retepores, the openings in the net-work are called fenestrules--the spaces between the ends, _dissepiments_--and those between the fenestrules, interstices. A delicate fossil retepore from the mountain limestone of Yorkshire (_R. flexa_), is figured _Lign. 89, fig. 13_.

Fenestrella.--Cells very small, indistinct externally, with small prominent openings; polyparium stony, fixed at the base, composed of branches, which inosculate by growth, and form a cup. Numerous delicate corals, formerly arranged as _Reteporæ_, occur in the Silurian rocks, and have been placed in this genus by Mr. Lonsdale. (_Sil. Syst._ p. 677.)

Petalæpora pulchella.[254] _Lign. 69, fig. 1._--This beautiful cretaceous coral is "tubular, free except at the base; framework composed of vertical laminæ, with an intermediate foraminated structure; apertures to the tubular cavities distributed over the surface; exterior varying with age." It has slender round dichotomous branches, and the polyparium when entire must have formed an elegant plexus of coral. A layer an inch thick, full of branches of this zoophyte, is exposed on the face of the chalk cliffs, near Dover; and beautiful masses, several inches square, made up of this coral, Idmonea and Pustulopora, may be obtained. The microscopic specimen figured in _Lign. 69_, was obtained with many other corals by washing chalk with a brush, and examining the detritus deposited.

[254] Mr. Lonsdale. Dixon's Fossils, p. 285.

Pustulopora. _Lign. 89, fig. 8._--Another very common tubular branched coral of the Dover chalk; the tubes are cylindrical, their apertures are arranged in annular or spiral rows, and slightly projecting, giving a pustulous appearance to the stem and branches. Specimens covering a piece of chalk six or eight inches wide, and a foot long, have been discovered. The example figured is a very minute branch.

Homœsolen ramulosus.[255] _Lign. 89, figs. 9, 11._--This delicate branched coral is formed of large and small tubes variously intermingled, both inclined in the same direction, partially visible on the surface, or wholly concealed, limited to one side of the coral; mouths simple tubular extremities; back without pores, composed of a continuous lamina.[256]

[255] Homœsolen, from ομοιος, similar; and σωλην, a tube.

[256] Mr. Lonsdale, in Dixon's Fossils, p. 307, tab. xviii. B. figs, 3, 4, 5.

The elegant coral, _fig. 11, Lign. 89_, is thus named by Mr. Lonsdale; it resembles his _fig. 4_. The fossil, _fig. 9, Lign. 89_, though very different in its branching, and in the surface, which is covered with pores, is evidently identical with _fig. 3_ of Mr. Lonsdale, which he refers to the same species.

Idmonea, _Lign. 89, fig. 6._--In this elegant coral the polyparium is calcareous, branched, porous; the cells distinct, prominent, arranged in single rows, more or less inclined, on each side a median line on the inner face only. The genus is extinct.

A beautiful species of Idmonea, of which a small branch is figured in _Lign. 89_, abounds in the chalk of Kent and Sussex; it often forms a cluster, two or three inches in circumference. The surface of the stems is covered with minute pores, and the cells are distinct, and placed in single rows; the left-hand figure of _fig. 6_ shows the plain surface, and that on the right, the opposite and inner, each margin of which is garnished with a row of cells; a portion magnified is represented _fig. 12_.[257]

[257] In the former edition of this work, I named this species _I. Dixoniana_, to commemorate the researches of my late friend, Frederic Dixon, Esq., of Worthing, who had formed an interesting collection of chalk fossils, and announced a work on the "Zoology of the Chalk Formation," to be richly illustrated with figures of many undescribed organic remains. It appears that a species, supposed to be identical, had been previously named by Mr. Milne Edwards, _I. cretacea_. See Dixon's Foss. tab. xviii. A. _fig._ 5, p. 281. Mr. Lonsdale places it in a new genus, with the name of Desmeopora semicylindrica. It will convey some idea to the unscientific reader, of the labour bestowed on this department of palæontology, to learn that the description and identification of but 25 species of minute corals, represented on three plates, occupy ninety pages of close printing in royal 4to. of Mr. Dixon's work.

Idmonea Comptoniana,[258] _Lign. 89, fig. 14._--This is a very small and remarkable coral; it is dichotomous, cylindrical, with elongated distinct cells, which are disposed in triplets, at regular distinct intervals, on one side of the stem.

[258] This specific name is in honour of the noble and highly respected President of the Royal Society, the Marquess of Northampton. 1844.

We have now described all the fossil corals figured in _Lign. 89_; and have shown what interesting organisms may be detected in a few grains of calcareous earth. It would be easy to give restored figures of the beings whose stony skeletons are the subject of these remarks, from their close resemblance to existing species; every pore and cell might be represented fraught with life; here the agile inmates, with their little arms fully expanded, and in rapid motion; there retreating within their recesses, and devouring the infinitesimal living atoms that constitute their food; or rapidly shrinking up their tentacula upon the approach of danger; even their varied colours might be introduced, and thus the beautiful and highly interesting picture drawn by the imagination, of a group of living zoophytes of the ancient chalk ocean, be presented to the eye.

Although, for convenience, I have selected the above examples principally from the cretaceous strata, the reader must not suppose that other deposits are not equally prolific in these remains. The Coral-rag of the Oolite, many beds of the Mountain limestone, and those of Dudley and Wenlock of the Silurian System, contain myriads of minute polypidoms associated with the coralline masses of which we have already treated. Exquisite figures of the Silurian corals, by Mr. Scharf, are given in _Sil. Syst._ pl. xv. xvi. and described by Mr. Lonsdale. A slab of the Dudley limestone often has the entire surface studded with minute corals of many species and genera, lying in bold relief, and in an admirable state of preservation.

Verticillipora (_Lign. 70, fig. 4. Lign. 72, fig. 3_).--Cells poriform, arranged in meshes on the surface of convex imbricating plates round a hollow axis, forming a fixed, irregular, subcylindrical polyparium. _Lign. 70, fig. 4_, represents a coral often met with in the gravel-pits at Faringdon, (_ante_, p. 228,) which is referred by Mr, Morris to this genus. It is composed of short cylindrical anastomosing tubular branches, emanating from an expanded base, divided internally by transverse parallel plates, covered with exceedingly minute pores or cells, disposed in meshes; the plates surround a hollow axis; the structure is well shown in the figure.

Lunulites. _Lign. 70._--The polyparium is stony, orbicular, convex above, concave below; concavity radiated; convexity covered with cells, arranged in concentric circles on diverging striæ.

A species of this coral is often found in the chalk: _Lign. 70, fig. 1_, represents a specimen from the South Downs, discovered by Mr. Walter Mantell. The natural affinities of this genus are not determined with precision; but I have placed it with the Bryozoa in accordance with the opinion of M. de Blainville. It is an elegant white coral, and easily recognized among the minute organisms of the chalk.

* * * * *

[Sidenote: DISTRIBUTION OF FOSSIL BRYOZOA.]

Geological Distribution of Fossil Zoophytes.--Although the geological distribution of fossil zoophytes affords less striking phenomena than that of the vegetable kingdom, yet some interesting reflections are suggested by the facts we have thus cursorily noticed. We find that in the most ancient seas of which any vestiges of their inhabitants remain, these forms of vitality existed, and produced the same physical results as at the present time; giving rise to coral-reefs, and banks of coral-limestones, and largely contributing to the solid materials of the crust of the globe. Nearly 400 British species are enumerated by Mr. Morris, and the list has subsequently been greatly extended by the labours of Phillips, Portlock, Lonsdale, McCoy, Milne Edwards, and other eminent naturalists.

The Tertiary formations afford numerous species of Caryophylliæ, Flustræ, Escharæ, Spongia, &c.; and the _Crag_, several genera that are as yet but imperfectly determined. The older Tertiary, or Eocene deposits, contain Turbinoliæ, Astreæ, Fungiæ, Meandrinæ, and species of other genera, the recent types of which are inhabitants of tropical seas.

The zoophytes of the British Chalk have been illustrated in detail by Mr. Lonsdale in Dixon's Cretaceous and Tertiary Fossils of the South-East of England; and by Dr. Milne Edwards in the Monographs of the Palæontological Society.

In the Maestricht deposits, lamelliferous corals, as Astreæ, Fungiæ, Meandrinæ, &c. prevail, and may be extracted from the friable arenaceous limestones in a fine state of preservation. In the White Chalk and Greensand of this country, the Spongites and allied genera are abundant, and associated with Caryophylliæ, Astreæ, and many forms of Bryozoa.

But in the cretaceous formation of England, no coral-reefs are observable; the zoophytal remains, with but a few local exceptions, occur promiscuously intermingled with the fishes, shells, Radiaria, and other marine exuviæ; although many layers, or thin seams of chalk and marl, are largely composed of the detritus of corals, like the modern deposits of the Bermudas (_Wond._ p. 613). These phenomena are in accordance with the lithological characters of the White Chalk strata, and the nature of its mollusca, both of which indicate a deep sea; and coral-reefs are only formed at moderate depths. But in regions where the sea was shallow, during the deposition of the cretaceous rocks, beds of coral limestone were produced; and these also contain littoral (sea-shore) shells, associated with the usual sponges and zoophytes (_Wond._ p. 613).

In the marine secondary formations antecedent to the cretaceous, namely, the Lias and Oolite, coral-reefs, which appear to have undergone no change save that of elevation from the bottom of the sea, and the consolidation of their materials by mineral infiltrations, demonstrate a condition of the ocean in our latitudes, which is now only met with in the tropics (_Wond._ p. 614).

The limestones of the Carboniferous, Devonian, and Silurian formations, abound in anthozoan corals, and among them are many kinds of Cyathophyllum, Lithododendra, Syringopora, Catenipora, Graptolites, &c., which are characteristic of these deposits.

The Silurian zoophytes are figured in _Sil. Syst._; and the splendid works on the British Palæozoic Fossils, by Prof. Sedgwick and Prof. McCoy, now in course of publication, contain many admirable figures of new, or but imperfectly known species.

The extensive beds of coralline limestones, which are found in the Silurian strata, wherever they occur,--for the limestones of this system in North America are characterized by the same species of corals as those of England,--seem to indicate that a more equal temperature prevailed throughout the ocean, at that geological epoch, than at the present time, when the geographical distribution of the coral zoophytes is strictly limited by temperature. The reef-forming genera are now confined to waters where the temperature is not below 70°; their most prolific development being 76°. The apparent exception, the occurrence of coral-reefs at the Bermudas, is found to depend upon proximity to the Gulf Stream (_Wond._ p. 614), which brings down the thermal waters of the tropics, and increases the local temperature of the sea in those localities.[259]

[259] Mr. Deane's splendid and masterly work on Corals, should be studied by those who wish to be acquainted with the present state of this branch of natural history.

[Sidenote: ON COLLECTING FOSSIL CORALS.]

On Collecting Fossil Corals.--Few instructions are required for the collection of fossil zoophytes; for as the most important characters of the several kinds have been pointed out in the previous descriptions, the student will be able to select illustrative specimens for his cabinet. The minute corals, &c. of the Chalk, and other limestones, are to be obtained by the same process as that directed for the discovery and preservation of the foraminifera, and other microscopic organisms, at the end of the next chapter. The larger examples should be left attached to a piece of chalk, when practicable, and the surrounding stone removed with a knife or graver, so as to expose as much of the fossil as may be required for the display of its characters, without loosening its attachment to the block. When the investing chalk is very hard, frequently pencilling the specimen with vinegar, or dilute hydrochloric acid, will soften the stone, and render its removal easy, by means of a soft brush: when acid is employed, the specimen must afterwards be well rinsed in cold water.[260]

[260] It may be well to caution the collector against employing sulphuric acid (commonly called _oil_ of _vitriol_) for this purpose, for a white insoluble deposit (sulphate of lime) will thus be formed on the specimen, and its appearance irremediably injured. Many of the fossil corals obtained from the chalk of Dover Cliffs, are so saturated with muriate of soda, from long exposure to the spray of the sea, as to be liable to decomposition in the course of a few weeks, and are therefore not worth purchasing of the dealers.

The zoophytes that are in part flint, and part chalk, as the Ventriculites, (_ante_, p. 244, _Lign. 81_,) can rarely be obtained, except through the quarrymen who have been instructed how to extract them from the rock. The first specimen of this kind that came under my notice, I discovered while breaking a mass of chalk, in search of fungiform flints; when, to my great delight, I found the fossil, _Lign. 81, fig. 3_, by which at once, and for the first time, was shown the connexion between the chalk specimens, _Lign. 8, figs. 1, 2_, and the flints figured in _Lign. 8, figs. 2, 3, 6, 7, 8_. Upon showing this fossil to the quarrymen, and exciting their attention by suitable rewards, I obtained the illustrative series now in the British Museum.[261] Much light would be thrown on the nature of other zoophytes of the chalk that are invested with flint, if due care were taken in the collection of specimens, and they were examined before extracted from the rock. Loose, delicate specimens, whether from the chalk or tertiary strata, should be affixed with strong gum-water to cards, or pieces of thin board, covered with coloured paper.

[261] Petrifactions, Room VI. p. 466.

The Greensand Spongites, Siphoniæ, &c. may often be extracted from the rock tolerably perfect, by a well-directed blow of the hammer; but fragile species should be left attached to a block, and the surrounding stone be carefully chiselled away, so as to expose the most essential characters.

The Faringdon zoophytes are, for the most part, encrusted by an aggregation of minute polyparia, shells, and detritus, which may be partially removed by washing with a stiff brush, and their cavities cleared with a stout penknife, removing the extraneous matter by _chipping_, not by scraping, or the surface will be injured. In this manner the beautiful specimens figured, _ante_, p. 228, were developed.

The Corals in the hard limestones can seldom be chiselled out to advantage; for the most part, polished sections best exhibit the form and structure of the originals.

Weather-worn or water-worn masses of coral limestone often display the structure of the zoophytes of which they are in a great measure composed, in a beautiful state of sculpture and relief: the silicified or calcified corals appearing as perfect as if fresh from the sea. The mural rocks of coral limestone at Florence Court, the seat of the Earl of Enniskillen, are in many parts encrusted, as it were, with syringopora and other tubular corals, laid bare uninjured by the long and insensible effect of atmospheric erosion. A beautiful illustration of the old aphorism,--"Aqua cavat lapidem non vi sed sæpe cadendo,"--is afforded by the splendid examples of cateniporæ, fungiæ, caryophillæ, sculptured in alto-relievo on the face of the Silurian rocks over which dash the rapids at the Falls of the Ohio.

The silicified zoophytes of the West Indies, and those from Ava and the Sub-Himalayas, form beautiful subjects for the microscope; and chips, or sections, should be prepared in the manner recommended for fossil wood in the same state of mineralization.

[Sidenote: LOCALITIES OF FOSSIL ZOOPHYTES.]

British localities.--The gravels and sands of the Crag afford most favourable sites for obtaining tertiary zoophytes.

In the London clay at Bracklesham Bay, a species of Astrea (_A. Websteri_) is often met with attached to flints and pebbles.

In the Greensand of Atherfield, in the Isle of Wight, an elegant coral (_Astrea elegans_) is by no means rare.

The Greensand gravel-pits, near Faringdon, in Berkshire, abound, as already mentioned, (_ante_, p. 228,) in many kinds of sponges, and other porifera; and the quarries of oolitic limestone in the vicinity of that town, yield the usual corals of the Jurassic formation in great profusion, I know of no locality richer in fossil zoophytes, than Faringdon.[262]

[262] See Excursion, Part IV. of this work.

The quarries of that division of the Oolite called Coral-rag (as in the north-west of Berkshire, Oxfordshire, Gloucestershire, &c.), afford the usual corals of the Oolite.

The Oolite near Bath contains many species, and large masses of a minute coral (_Eunomia radiata_), are abundant.

At Steeple Ashton, in Wiltshire, numerous oolitic corals may be obtained. The silicified _Astreæ_, of Tisbury, in the same county, deserve particular notice (_ante_, p. 263).

Clifton, near Bristol, and Torquay and Babbicombe, on the Devonshire coast, are celebrated for their coralline marbles and pebbles; and many of the Derbyshire limestones are equally prolific in similar remains. The Devonian marbles are so largely employed for ornamental purposes,-- as brooches, tables, and side-boards,--that the figures produced by the sections of the enclosed corals must be familiar to the reader.[263]

[263] Specimens of these fossil corals, either as objects of natural history, or as ornaments, may be obtained of Mr. Tennant, 149, Strand.

Dudley, Wenlock, and Ludlow, are well known for the abundance and variety of Silurian polyparia.

Other localities of British corals have been mentioned in the course of this review of fossil zoophytes.