Chapter VII (1)

FOSSIL ZOOPHYTES.--PORIFERA OR AMORPHOZOA--POLYPIFERA OR CORALS--BRYOZOA OR MOLLUSCAN ZOOPHYTES.

Many tribes of the extraordinary beings whose mineralized relics are the immediate subject of our investigation, have largely contributed to the solid materials of which the sedimentary strata are composed. In the most ancient rocks in which vestiges of organic structures have been detected, those of _Zoophytes_ hold a conspicuous place; and in the seas of tropical climates, the agency of the Coral-animalcules, or Polypifera, is producing enormous deposits, and laying the foundations of new islands and continents, and forming reefs of rocks hundreds of miles in extent, which, if elevated above the level of the sea, would rival in magnitude the mountain-chains of modern Europe.

The reader unacquainted with the natural history of these marvellous creatures will find an account of their nature and economy, and of the physical effects produced on the earth's surface by their agency, in the sixth lecture of _Wond._ vol. ii. p. 588.

The term Zoophytes, or animal-plants, comprises two very distinct classes of living beings, namely, the Porifera, or Sponges, which (if not vegetables) are wanting in many attributes regarded as essential characteristics of the members of the animal kingdom; and the Polypifera, or polype-bearing-animals,--the Corals; which are generally associated groups or aggregations of individuals, united by a common organized mass or axis, each polype having an independent existence, and exhibiting volition and perception, in a greater or lesser degree.

Fossil Porifera.

[Sidenote: FOSSIL PORIFERA.]

The terms _Amorphozoa_ (signifying animals of variable shapes), and _Porifera_ (structures traversed by pores or channels), are employed by naturalists to designate the Sponges and analogous organisms, which appear to occupy the boundary line that separates the animal from the vegetable kingdom. The true position of the Sponges in the great system of Creation is still a disputed point; for while many distinguished naturalists regard them as _Protozoa_, or the lowest type of animal organization, others of equal eminence affirm that neither in structure nor functions do they differ from vegetables in any essential particular; and that if a line be drawn between the two kingdoms the Porifera must be placed on the vegetable side of the boundary. On the other hand, Dr. George Johnston, in his delightful work on the British Zoophytes,[193] expresses his opinion that there is nothing to discountenance the belief that these bodies hold an intermediate place; that they are, in fact, the true _Zoophytes_, or animal-plants; in some forms, as the green _Spongillæ_ of our lakes, the vegetable nature prevails; while in others, as the horny or keratose sponges filled with mucilaginous slime, and the fleshy _Tethya_ whose oscula, or pores, are said to exhibit signs of irritability, the animal character predominates.

[193] A History of British Sponges, &c. by Dr. George Johnston, Edinburgh. 1843. One vol. 8vo. with twenty-five plates. A previous work, "A History of British Zoophytes," with forty-four plates, from drawings by the accomplished lady of the Author, cannot be too highly commended.

Without committing ourselves to either opinion, and simply remarking that the large proportion of silex that enters into the tissues of a considerable number of the porifera, is more characteristic of vegetable than of animal structures, we proceed to consider the fossil sponges and allied forms, as the mineralized remains of the lowest types of the animal kingdom: if the vegetable nature of the originals were generally admitted, this section should have followed that which treats of the Diatomaceæ (_ante_, p. 100).

Sponge consists of a reticulated fibrous mass, covered with numerous pores of various sizes, which are connected internally by anastomosing channels, and this tissue is surrounded by a cellular gelatinous matter, by which the entire structure was secreted, and is, in fact, the vital part of the zoophyte. The tough framework or skeleton is in some kinds fibrous, horny, flexible, or rigid, and strengthened by calcareous or siliceous spicula (_spines_);[194] while in other species its substance is calcareous, and in some siliceous, constituting a web of transparent rock crystal, resembling spun glass,[195] The gelatinous matter lines all the cavities, and forms the margins of the openings; it presents no signs of irritability, and may be easily pressed out of the porous mass with the hand, so slight is the connexion between the skeleton and the investing tissue. Currents of water constantly enter the small pores, traverse the inosculating canals, and issue from the larger orifices, which often project above the surface in perforated papillæ. By the circulation of the water through the porous structure, the nutrition of the organized mass is effected; and the modifications observable in the number, size, form, and disposition of the pores, channels, and orifices, in different species, appear to be subservient to this especial purpose; the imbibition and expulsion of water being the only function the sponges perform. In its earliest stage the sponge gemmule is of a spheroidal shape, and covered with vibratile cilia, and after expulsion from the canals in which it is formed, moves rapidly through the water till it becomes attached to some body, and is then immovably fixed during life; exhibiting no signs of vitality save the aqueous circulation through the pores and canals.

[194] The Mediterranean and American sponges of commerce are devoid of spicules, and are deprived of their soft animal matter simply by washing freely in fresh water.

[195] I particularly allude to a siliceous Sponge from Barbadoes, named, by Mr. Samuel Stutchbury, formerly of the Bristol Institution, (now of Australia.) _Dictyochalix pumicea_. This specimen is of a fungiform shape, and appears to the naked eye as if formed of pumice stone, but under the microscope is literally a tissue of transparent silex.

There is much confusion in the arrangement and nomenclature of the fossil species of this class of zoophytes; and this has originated, in part, from the varied forms assumed by the same species, having been described under different names; and from the reprehensible practice of changing, without sufficient reason, the name assigned to a species by the original discoverer; an evil, unfortunately, not restricted to this department of natural history.

The recent Sponges are arranged in four groups according to their structure, viz.--

_Fresh-water Sponges._

Spongilla: siliceous spicula in a translucent jelly-like mass.

_Marine Sponges._

Tethea: having a tough outer skin; siliceous spicula in bundles, and radiating from the compact nucleus to the periphery.

Halichondria: (from _silex_ and _cartilago_) siliceous spicula in a cartilaginous mass.

Grantia: calcareous spicula in a gelatinous mass.

[Sidenote: FOSSIL SPONGES.]

M. D'Orbigny seems to believe that with the exception of the horny _Cliona_, all the fossil sponges had originally calcareous skeletons,--"qu'ils n'ont jamais été cornés, mais que leur tissu a toujours été calcaire et pierreuse;"[196] which is certainly not the case, for abundant examples of fossil keratose sponges occur.

[196] Cours Elémentaire de Paléontologie, torn. ii. p. 208.

I have selected a few genera for the illustration of the subject, and shall describe them under the names that are most familiar to the British scientific collector: doubtless sooner or later some competent naturalist will undertake the elucidation of this department of palæontology, and construct a classification and nomenclature based on natural characters; till then the student will find it hopeless to attempt to learn the ever-varying names of genera and species applied to fossil Porifera and Polypifera, by different observers.[197]

[197] It has happened most unfortunately, that but recently Mr. Lonsdale, in the late Mr. Dixon's beautiful work on Chalk and Tertiary Fossils, and Mr. Milne Edwards in his able Monograph in the Palæontological Society's Memoirs, have described many of our chalk Corals under different specific and generic names.

[Sidenote: SPONGITES IN CHALK AND FLINT.]

On the Sponges in Chalk and Flint.--From the durability of the tissue of the flexible sponges, and the imperishable nature of those which have a siliceous or calcareous endo-skeleton or framework, their fossil remains generally occur in a fine state of preservation, and in immense quantities, in the sediments that were deposited in those parts of the ancient sea-bottoms, originally inhabited by these zoophytes. Even the relics of the keratose species, the _Halichondria_, whose structure consists of siliceous spines imbedded in a cartilaginous mass, are equally abundant. Sponge-spicula are everywhere met with in the chalk, flint, and greensand, and many layers in the cretaceous strata are almost entirely composed of them.

Sponges so commonly form the nuclei of the nodular flints, that some naturalists have ascribed the formation of the layers and nodules of silex in the cretaceous rocks to these zoophytes: a supposition altogether groundless,[198] The various states of mineralization in which sponges occur in the chalk give rise to many beautiful and highly instructive fossils, as we shall point out in the course of this notice. In general the zoophyte is simply invested by the flint, the pores and tubes being filled with silex, the original tissue appearing as a brown reticulated calcareous mass. In other examples the sponge has been permeated by the liquid flint, and subsequently perished; and in this manner have been formed those hollow nodules which on being broken are found to contain only a powder, consisting of siliceous spicules and fragments of silicified sponge. But in numerous instances the substance of the zoophyte is completely silicified, and the intimate structure of the original exquisitely preserved; such are many of the flint-pebbles, and moss-agates, that are mounted as brooches and other ornaments.

[198] See Wonders of Geology, p. 300. This question is fully considered in a Memoir entitled Notes of a Microscopical Examination of the Chalk and Flint of the South-East of England, &c. by the Author, in 1845.

Spongites.[199]--This name I would apply generically to those fossils which appear to be identical in structure with the ordinary marine sponges that consist of a fibro-reticulated porous mass, destitute of regular tubes or canals: the form exceedingly various.

[199] _Achilleum_ of Schweigger.

The fossil sponges of the chalk may be divided into two groups; the cyathiforms, or cup-shaped, and the ramose, or branched. Flints inclosing the first kind, generally exhibit externally the form of the original; those containing the branched species are of irregular shapes, and except by an experienced observer, the nature of the enclosed body would not be suspected. On breaking them, the sponge is often well displayed, as in the specimen figured in _Lign. 69, fig. 2_: the surface of this fossil was covered with a white gritty powder, made up of minute needle-shaped siliceous spicula.

[Sidenote: SPONGITES IN FLINTS.]

Spongites Ramosus.--A branched sponge, sometimes from twelve to fifteen inches long, is not uncommon in the flints of the Lewes and Brighton chalk; the stems and branches are cylindrical, and the terminations of the latter are rounded and full of large pores. When completely silicified the structure can only be detected by fracture, but occasionally the sponge appears to have been saturated with liquid chalk before it was enveloped in the flint; and as it is coated with calcareous matter, it may be detached from the nodule entire.[200]

[200] In this manner I obtained the beautiful specimen (now in the British Museum) figured in my Foss. South Downs, tab, xv. fig. 11. A branch of this species is represented Pict. Atlas, pl. xxxix. fig. 12.

_Spongites lobatus_ (sp. Fleming) is figured Pict. Atlas, pl. xxxix. fig. 6.

_Chalk. Sussex._

Fig. 1.--Petalopora pulchella. Upper figure × ×: lower figure, _nat._
_Chalk near Chichester._ (_Mr. Walter Mantell._)

2.--Spongites clavellatus. a branch in the cavity of a flint.
_South Downs._

3.--Siphonia Morrisiana. (G. A. M.) A transverse polished section
of a pebble. _Brighton Beach._
]

A smaller ramose spongite, with numerous short clavate protuberances, is often met with in the flints of Sussex and Wilts; a branch is figured in _Lign. 69, fig. 2_.[201]

[201] This spongite is named Polypothecia clavellata, in Miss Benett's Wiltshire Fossils.

Spongites Townsendi. (_Pict. Atlas_, pl. xli.)--The cyathiform flints, whose shape depends on the inclosed zoophytes, so much resemble the cup-shaped sponges of commerce, as to be easily recognized in the heaps of nodules that are collected in chalk districts for the roads; they are from one to eight inches in diameter at the upper part, and many are of a globular or spheroidal shape; the surface has the usual calcareo-siliceous coating of flint nodules, giving a sensation of roughness to the touch; the margin of the cup generally exhibits a narrow band of porous structure, and when broken, sections of the enclosed body are exposed. These funnel-shaped spongites terminate at the bottom in a peduncle, whence fibrous root-like processes diverge; by these appendages the original was fixed to the rock. I have collected a few specimens in which the roots are attached to a shell, or pebble, but have never seen any that appeared to occupy the spot on which they grew. They seem to have been detached from their native sites by the waves, and transported to a distance, and subsiding into the tranquil depths of the ocean, became imbedded in the cretaceous sediments that were accumulating at the bottom.

Spongites (?) labyrinthicus.[202] _Lign. 80, fig. 5._--Another abundant species of amorphozoa has given rise to sub-hemispherical flints, rounded below and flat above, with a marginal band of porous tissue, that expands into flexuous lobes which fill up the area of the upper surface. When found imbedded in the chalk, the form of this zoophyte is often preserved entire; the upper part showing the lobated and flexuous character of the original. Upon breaking these flints, the organic structure is generally apparent; but in many instances has perished, and left a cavity which is either partially filled with stalactitical chalcedony, or lined with quartz crystals. These fossils vary in size from a walnut to that of an orange; the pedicle has long processes.

[202] Foss, S. D. tab. xv. _fig._ 7.

A lobed zoophyte, resembling the above in its general form, and long rootlets, is distinguished by a large central cavity, which is continued above the body in the form of a cylinder.[203]

[203] Beautiful figures of these and other chalk zoophytes are given by Mr. Toulmin Smith in his elegant memoir "On the Ventriculidæ." The specimens above described are named _Bracholites_ by Mr. Smith. The plan of the present work forbids the discussion of that author's opinions and inferences.

Spongites (?) flexuosus. _Lign. 80, fig. 10._--Among the cyathiform flints that abound in the chalk, a very elegant species is distinguished by a flexuous band that runs round the margin, and indicates the lobed structure of the original.

In the chalk of Flamborough Head, Yorkshire, many beautiful cyathiform sponges are preserved, in which the outer surface is thickly covered with projecting hollow papillæ; these fossils are generally silicified, the surface and pores being frosted over with minute quartz crystals. The museum of the York Institution contains a splendid series of these spongites.[204]

[204] The silicified state of these zoophytes was first detected by Mr. Charlesworth, who by immersing specimens in dilate hydrochloric acid, obtained admirable examples of the delicate structure of the original.

[Sidenote: FOSSIL ZOOPHYTES OF FARINGDON.]

Fossil Zoophytes of Faringdon. _Lign. 70, 71, 72._--The richest locality for fossil sponges in England is in the immediate neighbourhood of the little town of Faringdon, in Berkshire.[205] The Greensand beds that overlie the Oolite in that district, consist of a coarse friable aggregation of sand, comminuted shells, corals, amorphozoa, and echinoderms, more or less consolidated by a ferruginous cement. The gravel-pits, as the quarries are locally termed, expose what evidently were banks of detritus thrown up on the strand of a sea-margin; among the water-worn and fragmentary relics of oolitic as well as cretaceous forms, many perfect sponges of various kinds may be collected in the course of a few hours. Figures of some of the common species are subjoined.

[205] See Excursions, in vol. ii.

Fig. 1.--Lunulites radiatus. _Preston Chalk-pits_; view of the convex
side. (_Mr. Walter Mantell._)
1_a_.--Front view; _nat._
1_b_.--Portion of the surface of fig. 1, magnified.

2.--Scyphia intermedia; 1/2 _nat._ _Faringdon._

3.--Lithododendron sociale: the left-hand branch shows a vertical
section at the upper part, displaying the internal structure;
1/2 _nat._ _Mountain Limestone, Yorkshire._

4.--Verticillipora anastomosans. _Faringdon._

5.--Scyphia ramosa; 1/2 _nat._ _Faringdon._

6.--Scyphia foraminosa; 1/2 _nat._ _Faringdon._

7.--Cnemidium astrophorum; 1/3 _nat._ _Faringdon._
]

Scyphia. _Lign. 70, 72._--These spongites are of a tubular, fistulous, or cylindrical form, and terminate in a rounded pit; they are either simple or branched, and composed of a firm reticulated tissue; _Lign. 70, fig. 2, 5, 6_, and _Lign. 72, fig. 4_, are examples. The Upper Greensand at Folkstone and Dover abounds in a flexuous species, named Scyphia meandrina (_Morris_).

Cnemidium (_Goldfuss_). _Lign. 70, fig. 7._--These sponges consist of a cluster of turbinated projections, having a central pit above, and being porous on the external surface, and radiated at the margin. The mass is dense and fibrous, and is traversed by horizontal canals, diverging from the centre to the circumference.

(_Chenendopora fungiformis._)

_Greensand. Faringdon._]

Chenendopora.[GX] _Lign. 71._--The species of porifera thus named are cyathiform, or cup-shaped; externally furrowed, mamillated, or lobed; internally smooth, and the surface covered with fine pores. The beautiful species figured (_C. fungiformis_) is abundant in the gravel-pits, and well known to the quarrymen as "petrified salt-cellars."

[206] The Pictorial Atlas contains coloured figures of the following:--

Chenendopora fungiformis (_Michelin_), Pict. Atlas, pl. xliv. _fig._ 5:
according to Mr, Morris.

------------ subplana (_Michelin_), ibid, pl. xliv, _fig._ 3.

Scyphia articulata (_Goldfuss_), ibid, pl. xliii. figs. 7, 8, 9.

------- costata (_Goldfuss_), ibid. pl. xliv, fig, 1.

Cnemidium rimulosum (_Goldfuss_), ibid, pl. xliv. _fig._ 3.

_Greensand. Faringdon._

Fig. 1.--Tragos peziza.

2.--Probably Chenendopora in a young state.

3.--Verticillipora anastomosans.

4.--Species of Scyphia.

5.--Tragos Faringdoniensis.
]

Tragos. _Lign. 72, fig. 1._--These turbinated sponges are readily distinguished from the preceding, by the relatively large oscula, or open papillæ, disposed irregularly on the inner surface; as shown in the specimen, _fig. 1._ Their tissue is dense and fibrous. The fossil represented by _fig. 5_, though named Tragos by collectors, appears to differ in the structure of the inner surface from the type of this genus: it is a remarkably beautiful species.[207]

[207] It may be convenient to distinguish it as _T. Faringdoniensis_.

The base in all these Greensand sponges is flat and expanded; not fibrous and root-like, as in the spongites of the chalk previously described.

Among the shingle at Brighton, Margate, Dover, Isle of Wight, &c. pebbles containing fossil sponges may frequently be discovered. When the flint nodule has been broken, and the calcareous particles of the inclosed zoophytes are washed away by the action of the waves, a delicate silicified tissue remains.[208] Many of the large solid pebbles, are portions of silicified sponges, and polished specimens are beautiful objects under the microscope.

[208] The pebbles represented in Pict. Atlas, pl. xlv. fig. 5, 12, are specimens of this kind.

[Sidenote: SIPHONIA.]

Siphonia. _Lign. 73._--These fossil porifera are readily distinguished from those which have engaged our attention by their more symmetrical structure. The body of the zoophyte is a mass of dense porous tissue, of a pyriform or bulbous shape, supported by a slender stem fixed at the base by rootlets. The stem is composed of very fine parallel longitudinal tubes, which extend to a series of canals that traverse the mass, and terminate in openings on the surface of a shallow central cavity, as shown in the section, _fig. 2, Lign. 73_. The characters of this genus are well exemplified in a common species of the Greensand (_S. pyriformis_, _Lign. 73_), described by the late Mr. Webster, from specimens collected in the Isle of Wight, where it occurs in profusion, near Ventnor, and the Western lines. This zoophyte is pyriform, (_Lign. 73, fig. 1_,) and has a shallow cylindrical cavity, supported upon a long slender stem, the base of which is fixed by root-like processes (_fig. 5_); the transverse fracture shows a section of the longitudinal tubes. This species has been found in numerous localities of the Greensand, and also in the Firestone or malm-rock.[209]

[209] Dr. Fitton's figures, Geol. Trans. vol. ii. pl. xv. _a_, are very beautiful and accurate.

The Portland limestone contains numerous remains of a Siphonia closely resembling this species; and varied sections of its stems produce the white markings commonly observable on the slabs of pavements.

_Wilts, and Isle of Wight._

Fig. 1.--Siphonia pyriformis; the body or upper part.

2.--Vertical section of the same, showing the internal structure,
and the central cavity.

3.--Specimen of S. pyriformis in a young state.

4.--Siphonia (_Polypothecia_, of Miss Benett,) lobata; Firestone or
Upper Greensand, Warminster.

5.--The lower part of the stem, and radicles, of S. pyriformis.
]

A group of Sponges from the Upper Greensand, near Warminster, figured and described by the late Miss Etheldred Benett,[210] under the name of Polypothecia, comprises several forms that are allied in structure to the Siphoniæ. These fossils present considerable diversity of shape; one of the lobed forms is delineated in _Lign. 73, fig. 4_: and a branched species in _Lign. 74_. Upon breaking the stem of one of these zoophytes transversely, sections of parallel longitudinal tubes like those in the Siphoniæ are exhibited.

[210] An elegant Memoir on the Wiltshire Fossils, by this accomplished lady, is published in Sir R. C. Hoare's "Wiltshire."

Polypothecia dichotoma.

_Upper Greensand, Warminster, Wilts._]

The Kentish rag contains irregular ramose spongeous bodies, which belong to this group of porifera; and Mr. Bensted has discovered in his quarry, near Maidstone, numerous remains of a polymorphous lobed zoophyte, having a porous structure beset with spicula. In the Firestone of Southbourne, Steyning, and Bignor, in Sussex, I have observed large pyriform and subcylindrical Siphoniæ.

The organization of all these zoophytes was evidently adapted for the imbibition and circulation of sea-water, in a more perfect and definite manner than in the irregular simple sponges.

Flint-pebbles inclosing remains of Siphoniæ abound on the Sussex coast, especially in the shingle near Brighton, having been washed out of the chalk cliffs. There were several chalk-pits in Edward-street, (now, I believe, filled up and the area built upon,) in which every flint enveloped a sponge or siphonia; many specimens were mineralized by pyrites and beautifully exhibited the internal structure of the originals.

Siphonia Morrisiana. _Lign. 69, fig. 3._--A polished slice of a pebble from Brighton, whose markings are derived from the transverse section of an undescribed zoophyte is figured, _ante_, p. 224: though scarcely more than half the diameter of the original is preserved, yet its structure is well shown; the centre is occupied by numerous parallel openings, the sections of longitudinal tubes, and is surrounded by a broad zone of spongeous tissue.

I have seen many examples of this beautiful fossil, set for brooches in the jewellers' shops in the Isle of Wight, and at Brighton.[211]

[211] The specific name is in honour of John Morris, Esq. F.G.S. the author of the "Catalogue of British Fossils," whose important services to Palæontology and Geology it is gratifying thus to acknowledge.

There are coloured figures of Siphonite in Pictorial Atlas, pl. xxxix. _fig._ 9; pl. xlii. _fig._ 3, 4, 5, 7, 12, and 13; pl. xliii. _fig._ 6.

Siphoniæ (chiefly _S. pyriformis_) are abundant in the Upper Greensand, near Farnham in Surrey, but their tissues are saturated with phosphate of lime, instead of silica as is ordinarily the case; the entire sponge usually contains between 50 and 60 per cent, of phosphate: hence these fossils have, of late, been in great request for manure.[212]

[212] Mr. Payne, of Farnham, a distinguished agriculturist, has largely made use of them, both in the natural state and treated with sulphuric acid. The Firestone strata on St. Catherine's Hill, Isle of Wight, have been dug for a like purpose. See an "Account of the Phosphate Diggings," in my Isle of Wight, Second Edition, p. 448.

[Sidenote: CHOANITES KÖNIGI.]

Choanites Königi, _Lign. 75._--The zoophyte which has given rise to the fossils I have distinguished by the name of Choanites,[213] is of a spheroidal or sub-ovate form, and appears to have been composed of a softer tissue than the ordinary sponges. It has a central cavity, and was fixed at the base by long rootlets: its mass is traversed by numerous tubes or channels, which open on the inner surface of the cavity; it differs from Siphonia in not having a stem composed of bundles of tubes, and probably also in its constituent substance. Among the Sussex and Wiltshire chalk-flints specimens of this zoophyte are very common; they are easily recognized by the peculiar markings produced by the silicified tubes that radiate from the centre, as seen in _Lign. 75, fig. 4_. The semi-diaphanous pebbles on the Sussex coast, more frequently contain Choanites than any other zoophytes. From the beautiful and varied markings observable in the polished sections, they are in great request for brooches, and are termed _petrified sea-animal flowers_[214] by the lapidaries; among the shingle on the sea-shore at Bognor, Worthing, and other places, very fine examples may be collected.

[213] Foss. S. D. p. 178.

[214] From the supposition that the original was an _Actinia_, or _Sea-Anemone_. A coloured vertical section of a pebble of this kind is figured in my "Thoughts on a Pebble," Eighth Edition, pl. ii. See coloured figures of Choanites in Pict. Atlas, pl. xlii. _fig._ 1, 9, and 10; pl. xliv. _fig._ 8; and pl. xlv. _fig._ 10.

_Chalk, Lewes._

Fig. 1.--Transverse section of a siliceous specimen.

2.--Upper portion of a _Choanite_, in chalk, showing the opening
of the central cavity at _a_.

3.--Vertical section of a Choanite, in flint, exposing a section
of the mass, and canals passing obliquely from the
central cavity, through the substance.

4.--Choanite in flint; the usual appearance of these fossils.

5.--Various kinds of Spicula of fossil sponges; _magnified_.
]

_Lign. 75, fig. 4_, represents the usual appearance of a flint deriving its form from a Choanite; _fig. 2_, is the upper part of a Choanite preserved in chalk, and richly coloured by iron; the opening at the summit, _a_, is the orifice of the central cylindrical cavity, which is in this instance filled up by chalk, but in flint specimens, with silex of a different colour to that of the surrounding mass. If _fig. 2_, were placed on the top of _fig. 4_, the general shape of the original zoophyte would be represented. The opening at the base of _fig. 4_, marks the spot whence the processes of attachment proceeded. The vertical section of a flint, similar to _fig. 4_, is shown at _fig. 3_; and in this example are seen the central cavity, and a section of the substance of the zoophyte, which is traversed by numerous tubes, that ramify through the mass of which the body was composed, and terminate in openings on the inner wall of the central cavity, or sac. A transverse section of a similar flint is delineated in _fig. 1_; the central white spot indicates the sac filled with flint, and the tubes are seen radiating from it through the mass; under a powerful lens the interstitial structure appears to be granular rather than porous. The perfect transparency of the body when silicified, and the rich tints it has acquired from metallic solutions, and the compressed state in which it is often found, seem to indicate that the original mass was a soft gelatinous substance, like that of the _Actinia_, strengthened by spicula; for numerous tri-radiate spines, like those on the left-hand of _fig. 5, Lign. 75_, occur occasionally in chalk specimens.

In many Choanites, which differ in no other respect from the present species, vertical sections show on each side the central cavity, large oval spots, that are sections of a canal which traverses the entire mass, proceeding from the base to the summit, in a spiral coil around the central cavity. This structure was first detected by Mr. Cunnington. Mr. Woodward thinks this spiral tube is common to all the Choanites, and constitutes a generic character; but so many examples have passed under my examination in which no traces of such a canal are perceptible, that it may be a specific difference.

Among the chalk amorphozoa whose true affinities are doubtful, is a small turbinated zoophyte, which I would place provisionally under this genus; it has a shallow central cavity, with a broad smooth margin, a reticulated external surface, and radicle processes proceeding from the base; see _Lign. 80, fig. 1_.

[Sidenote: PARAMOUDRA.]

Paramoudra. _Lign. 76._--This vernacular Irish term was introduced by Dr. Buckland, in his account of some gigantic flints, thus popularly named, that occur in the chalk near Belfast, and also at Whitlingham, near Norwich. These fossils are of an irregular, oblong, spherical, or pyriform shape, having a cavity above, which, in some specimens, extends to the bottom; indications of a pedicle are seen at the base; in short, they closely resemble, upon a large scale, the funnel-shaped spongites, so frequent in the flints of the South Downs. Their appearance _in situ_, is represented _Lign. 76_, from Dr. Buckland's illustrations: _b_, is a single specimen, partly imbedded in the chalk, and _c_, _d_, two of the fossils in contact, the pedicle of the upper one lying in the cavity of the lower.

These bodies are from one to two or more feet in length, and from six inches to a foot in diameter. The appearance, both of the outer and inner surface, is that of the usual white calcareo-siliceous crust of spongitic chalk-flints. Upon breaking them, no decided structure is perceptible; but here and there, patches of red and blue chalcedony occur, as in the Ventriculites and spongites in chalk-flints; the originals were probably large goblet-shaped zoophytes, allied to the sponges, but of so perishable a nature as to leave but few traces of their organization, save their general form. Specimens may however yet be found with the structure preserved, for many years elapsed after the first discovery of flint ventriculites, before I obtained examples that threw light on their origin and formation.

(_The Very Rev. Dr. Buckland._ Geol. Trans, vol. iv.)

_a, a, a._ Layers of flint nodules, alternating with chalk strata,
_b._ A Paramoudra, imbedded in the chalk,
_c, d._ Two of these bodies in contact.
]

In the Devonian slates of Polperro some curious fossils, supposed to be remains of fishes, have been ascertained by Prof McCoy to be Amorphozoa, and are described by that eminent palæontologist under the name of _Steganodictyum_.[215]

[215] "Synopsis of the Classification of the British Palæozoic Fossils," by Prof. Sedgwick and Fred. McCoy. 4to. Fas. 2, p. vii. pl. 2 A. 1852.

Clionites (_Morris_) _Lign. 130._--A recent parasitical sponge (first described by Dr. Grant under the name of _Cliona_), consisting of a fleshy substance, full of siliceous tubular pin-shaped spicula, gives rise to those perforations with which oysters and other shells are often completely riddled,[216] Certain bivalve shells in the cretaceous seas appear to have been peculiarly obnoxious to the depredations of similar zoophytes, and in consequence of the cavities left by the decay of the sponge having subsequently been filled up by flint, a curious series of fossil bodies has resulted, which we shall more particularly notice hereafter. These fossils Mr. Morris has distinguished by the name _Clionites_, to indicate their origin; they are not, however, the silicified sponge, but inorganic casts, moulded in the excavations. The common species is _C. Conybearei_: "cells irregular, somewhat polygonal, with one or more papillæ; surface finely tuberculated; connecting threads numerous."[217]

[216] For an account of the characters of the recent Cliona, see a monograph by Mr. Hancock, Annals of Nat. Hist. May 1851.

[217] Ann. Nat. Hist. August 1851, pl. iv, fig. 8.

Spicula, or spines of Porifera. _Lign. 75._--Siliceous spicules, as we have had occasion to mention, occur in immense quantities in some of those deposits which abound in the remains of spongites. These spines are tubular, and of various shapes; some are acicular, or needle-like; others of a stellate form; many are tri-radiate or multi-radiate; and some have the shape of a trident; a few of these fossils are figured in _Lign. 75_. As the _Actinia_, _Gorgonia_, and _Alcyonia_, possess spicula, some of the fossil spines may have been derived from those zoophytes. The larger spicules may be discovered with a lens of moderate power, or even by the unassisted eye; but all will amply repay a microscopical examination, and the minutest can only thus be detected.

[Sidenote: SPINIFERITES IN FLINTS.]

(Seen by transmitted light.)

Fig. 1.--A thin-translucent chip of flint; _nat._

2.--The same magnified, and viewed by transmitted light; showing
a group of five Spiniferites.

3.--The same more highly magnified.

4.--Spin. ramosus; one of the animalculites seen in fig.
3, very highly magnified.

5.--Spin. Reginaldi; one of the same group; × 300
diameters.

6.--A variety of S. ramosus; another of the same cluster
of Spiniferites.
]

Spiniferites (_Xanthidium_, Ehrenb.). _Lign. 77._--I propose to describe in this place those elegant and very minute bodies, that occur in great numbers in the chalk and flint, and which, on the authority of M. Ehrenberg, were regarded as identical with the siliceous frustules of the genus of fresh-water Desmidiæ, named _Xanthidium_[218] (_ante_, p. 91.) Later and more correct observations have proved that the fossils under consideration entirely differ from their supposed homologues; their original substance not being siliceous, but flexible and membranous; and that instead of being spores of algæ, they are probably the gemmules either of porifera, or of polypifera.

[218] Several recent species of Xanthidium are figured in _Plate IV._ of this volume.

To avoid the perpetuation of the error by the retention of the botanical name of a recent genus of plants, for fossils whose vegetable origin is very problematical, and which are entirely distinct from their supposed analogues, I would substitute that of Spiniferites,[219] a term simply expressive of the general aspect of these bodies; that of a globe or sphere beset with spines. The appearance of these fossils will be understood by the examination of a group discovered by Mr. Reginald Neville Mantell, in a fragment chipped off from a flint pebble; and I will describe the mode by which these minute objects were detected, as it offers a good practical lesson for the young investigator.

[219] From _spina_, a spine, and _fero_, to bear.

The chip of flint is represented, of the natural size, in _Lign. 77, fig. 1_; it was immersed in oil of turpentine for a short time, and then placed on a piece of glass, and examined with a moderate power, by transmitted light, the turpentine having rendered the translucent flint almost as transparent as glass; this appearance is shown in _fig. 2_; the organisms here represented are from 1/300 to 1/500 of an inch in diameter. The half-inch object-glass was next employed, and _fig. 3_ gives the result. The quarter-inch object-glass, and a corresponding eye-piece, were then substituted, and by the adaptation of a camera lucida, _figs._ 4, 5, and 6, were delineated. As _fig. 5_ proved to be a new species, it was named after its discoverer.

The specimens in flint, when rendered transparent and viewed by transmitted light under a high power, as shown in _Lign. 78_, and 79, appear as hollow globular bodies, beset with spinous processes, which in most species are fimbriated at the extremities. There is considerable variety in the form and length of the spines. In _S. Reginaldi_, these appendages are numerous, regular, short, and relatively thick: in an elegant species discovered by the Rev. J. B. Reade (_Lign. 79_) they are long and palmated: in other kinds they are of intermediate size and proportions.[220]

[220] Excellent figures of several species are given in a Memoir by H. H. White, Esq. of Clapham, in the Trans. Microscopical Society, vol. i. p. 77.

Spiniferites Reginaldi.

(_Magnified 500 diameters_.)]

Spiniferites palmatus; in flint.

(× 500 _diameters_.)]

The apparently torn and collapsed state of the body and arms of some examples first led me to doubt the siliceous nature of the original substance; and on my discovery of the soft parts of foraminifera in flint and chalk, Mr. Deane undertook to search for the so-called Xanthidia in chalk, that these bodies might be subjected to chemical analysis,[221] Mr. Deane succeeded in detecting all the usual species in the Dover chalk, by digesting some chalk in dilute hydrochloric acid, and mounting the residue in Canada balsam. In this state the shape of the body is that of a depressed sphere; many of the specimens appear to have a circular opening, and the arms or spines to be closed at the extremities. Upon pressure under water between two pieces of glass, they were torn asunder as a horny or cartilaginous substance would be, and the spines in contact with the glass were bent. Some after maceration in water several weeks became flaccid; a proof that they are not siliceous.[222]

[221] A torn and apparently shrunken specimen from chalk, is represented in my paper on Foraminifera; _Philos. Trans._ 1846, p. 465.

[222] Memoir on Fossil Xanthidia, by Henry Deane, Esq. Microscopical Journal, 1846.

The real nature of these fossils must be regarded as still undetermined: their prevalence in the chalk-flints whose forms are derived from zoophytes, seems to countenance the supposition that the Spiniferites are the gemmules or early state of animals of this family; but I have never detected any organic connexion between them and the porifera with which they are associated; it is possible they may be the germs of the remarkable zoophytes we have next to examine.

* * * * *

[Sidenote: VENTRICULITES.]

Ventriculites.[223] _Lign. 80, 81, 82._--At every step of our review of the fossil zoophytes, I find myself embarrassed by the conflicting opinions entertained by naturalists, respecting some of the most abundant of the extinct forms; arising from the imperfect state of our knowledge as to the structure of the originals, which compels a comparison with recent types, from which, perhaps, the fossils differed essentially in their organization. This remark especially applies to the zoophytes which have given rise to the fungiform flints so well known to the inhabitants of the chalk districts of Sussex, as "_petrified mushrooms_," from their close resemblance in form to fungi: a specimen with this name inscribed on it in the cabinet of a friend first drew my attention to these curious fossils. In _Lign. 80, figs. 2, 3, 4, 6, 7, 8, 9_, several flints of this kind are represented; _figs._ 3, 6, 8, are fungiform; _fig._ 7, is the upper part of a specimen, the stem having been broken off; _figs._ 2 and 4, are examples of the lower part of the zoophyte; in all, there are openings at the base, and a groove on the margin or edge of the upper part in which the structure of the inclosed fossil is visible; upon breaking these flints, sections of a funnel-shaped body are exposed.

[223] Ventriculite; from _ventriculus_, a ventricle or sac.

_From the South Downs, near Lewes_; 1/6 _nat._

Fig. 1.--Choanites (?) Turbinatus.

2, 3, 4, 6, 7, 8, 9.--Flints, whose forms are derived from
Ventriculites, provincially called "_petrified mushrooms_."

5.--Spongites labyrinthicus.

10.--Spongites flexuosus.
]

The origin of these fossils will be understood by reference to the four specimens delineated in _Lign. 81_. In _fig._ 3, a fungiform flint, resembling _fig._ 6, of _Lign. 80_, is seen in the lower part of a cup-shaped zoophyte; while above, and surrounding the flint, the impression remains of the reticulated outer surface, deeply coloured by a ferruginous tinge. In _fig._ 4, _Lign. 81_, a small turbinated flint, resembling _fig._ 4, of _Lign. 80_, occupies the base, and three rootlets are seen emerging from it at a. In _Lign. 82, fig. 1_, in which the chalk has been removed so as to expose the outer surface of the Ventriculite, a flint occupies the centre at c; above which, the radiating reticulated structure is spread out on the chalk, _a_; the base, with its roots, is shown at _b_.

_Chalk; near Lewes._

Fig. 1.--A perfect specimen in chalk, inverted, showing the external
reticulated surface; the apex of the base projects in the
centre.

2.--Specimen expanded, displaying the inner surface, studded over
with the openings of the cells or tubes.

3.--A Ventriculite in chalk; the lower part inclosed in flint.

4.--Portion of a Ventriculite; the stem towards the base is
enveloped in flint, and three radicle processes spread from it
into the surrounding chalk at _a_.
]

These specimens demonstrate that all the flints referred to, have been moulded in the cavities of cyathiform zoophytes; and that their diversity of figure has arisen from the amount of silex that happened to permeate the organism; if but a small proportion of silica in solution was present, then flints, like _fig._ 4, were produced; if the quantity were sufficient to fill up a considerable part of the tissues of the original, fungiform flints, as _Lign. 80, fig. 3_, and _Lign. 81, fig. 3_, were the result. The disciform flints originated from the expanded examples, _Lign._ 81, _figs._ 1 and 2: and when the silex was insufficient to silicify the entire zoophyte, an annular flint, resembling a quoit, was formed.

_Chalk, near Lewes._

Fig. 1.--A specimen, in which the middle is inclosed in a flint _c_;
the external structure of the Ventriculite is seen at _a_,
expanded on the chalk; and the pedicle with its roots is
exposed at _b_. The figures are one-fourth the size of the
originals.

2, 3, 5.--Chalk specimens, showing the external structure of stems
of Ventriculites.

4.--A siliceous cast of the cavity of a Ventriculite covered with
papillæ, moulded in the orifices of the cells.
]

The form of the original was evidently that of a hollow inverted cone, terminating in a point at the base, which was attached by fibrous rootlets to other bodies. The outer integument was reticulated, that is, disposed in meshes, like net-work; and the inner surface studded with regular openings, apparently the orifices of tubular cells. The substance of the mass appears to have been sufficiently flexible to expand and contract without laceration. This opinion is based on the fact, that in many specimens the zoophyte is a nearly flat circular disc (_Lign. 81, figs. 1, 2_); and in others a subcylindrical pouch. In the former state the outer reticulated structure is elongated, while in the latter, it is corrugated; hence I am led to conclude that the original possessed a common irritability, and was able to contract and expand like many of the flexible polypiaria. The openings on the inner surface are cylindrical, and very regular; the flints often present sharp casts of them, which appear like rows of minute pillars. When the flint filling up the cavity of a Ventriculite can be extracted, it is a solid cone, studded with papillæ, the casts of the cells, as in _Lign. 82, fig. 4_.

In the flints, the substance of the Ventriculites is generally as translucent as that of the Choanites, and defined by its rich purple, sienna, or grey colour;[224] but towards the base and margin it is more or less calcareous; and in many examples the whole, or a large portion of the zoophyte, is in this state. But this fact does not invalidate the inference that the original was flexible; for in these instances the tissues may have been immersed in fluid chalk before their envelopment in flint,[225] The chalk specimens are commonly as friable and earthy as the surrounding stone, from which they are distinguishable by their ochreous colour.

[224] Pict. Atlas, pl. xlv. _fig._ 9, represents a beautiful transverse section of the lower part of a Ventriculite in flint, richly coloured. Pl. xliii. _fig._ 16, is a pebble containing the base of a Ventriculite; the orifices on the top have been produced by the transit of the radicle processes; for the fossil is drawn in an inverted position, a common error before the origin of these flints was ascertained.

[225] A piece of sponge dipped in liquid plaster of Paris, and afterwards inclosed in a transparent substance, as glass, would present such an appearance.

The stain always observable in the tissues of the chalk Ventriculites and other zoophytes, while the surrounding white limestone is uncoloured, may be explained by the chemical changes to which the decomposition of animal matter under such circumstances would give rise. If sulphuretted hydrogen were evolved from the putrifying zoophytes imbedded in calcareous mud containing iron in solution, the sulphur would enter into combination with the iron, the hydrogen escape, and a sulphate or sulphuret of iron be deposited, atom by atom, and thus impart colour and permanence of form to the original.

When the inclosed organisms in the flint nodules have perished, chalcedony, quartz crystals, or crystallized pyrites, sometimes of great beauty, are found occupying the cavities; in short, numerous modifications of the petrifactive process are beautifully exhibited in these common, but highly interesting, cretaceous fossils.

The species to which the previous remarks more immediately refer, is named _Ventriculites radiatus_; from the radiated appearance of the external integument; some of the expanded specimens are more than one foot in diameter.[226]

[226] The reader interested in the history of these objects should consult Foss. South Downs, p. 167, plates x, xi, xii. xiii. xiv. A memoir by the Author on these fossils, under the name of _Alcyonium chonoides_, with four beautiful plates, was published in the Linnæan Transactions, vol. xi. 1821. The _Ventriculites_ are the only organic remains figured in Conybeare and Phillips's Geology of England and Wales, p. 76.

_Ocellaria inclusa. König._

Fig. 1.--Portion of the surface of fig. 2, magnified.

2.--The fossil body extracted from the flint, fig. 4.
2_a_.--Transverse section of the same, showing a central
spot of flint, surrounded by tubular cells.
2_b_.--Two of the cells of fig. 2_a_, highly magnified.

4.--The hollow flint, from which fig. 2 was extracted; the papillæ
on the surface, are casts of the apertures of cells.
]

Ventriculites alcyonoides. _Lign. 83._--Under the name of "_Ocellaria inclusa_," the late Mr. König[227] figured and described an elegant fossil zoophyte not uncommon in the chalk and flints of Sussex. This fossil is inversely conical, and somewhat resembles the cast of the cavity of _Ventriculites radiatus_, but a little attention will enable the collector to distinguish it. The flint that is moulded in _V. radiatus_, is surrounded by the substance of the zoophyte, and if found detached, with the investing material removed, shows no structure whatever, but simply a surface covered with minute papillæ. The present zoophyte is generally included in a nodule, and by a slight blow may be readily separated from the surrounding flint; it then has the appearance of a white calcareous cone, beset with regular cells, disposed in quincunx order (_Lign. 83, fig. 2_); leaving a conical cavity in the flint, which is covered with corresponding eminences (_Lign. 83, fig. 4_). Upon breaking the cone itself, it is found to consist of a dense reticulated structure, from one-eighth to a quarter of an inch in thickness (_Lign. 83, fig. 2a_), investing a solid nucleus of flint, the surface of the latter being covered with minute points, which are less regular than those on the cavity of the outer case. The specific name, _inclusa_, was suggested by this character; which, however, is only accidental, for the specimens imbedded in chalk, are simply surrounded by the stone. It is the calcareous nature of the fossil, which renders it so easily separable from the investing flint, while its cells afford numerous points of attachment, and these remain as casts in relief on the interior of the hollow case: I have not observed the same regularity of structure on the inner as on the outer surface.

[227] Icones Foss. Sect. _fig._ 98.

The reticulated integument of this zoophyte resembles in structure that of _V. radiatus_. With regard to the latter, I should state that Mr. Toulmin Smith[228] discovered that the inosculating fibres of the intimate tissue formed an octahedral plexus at each knot or point of union; and this structure Mr. Smith regards as peculiar to the Ventriculites, and states that he detected it in all the fossils he has arranged under the name _Ventriculidæ_. No spicula have been detected in the integuments.

[228] "On the Ventriculidæ;" a series of papers published in the Annals of Natural History, with many figures of cretaceous zoophytes. By Toulmin Smith, Esq.

Until more ample and satisfactory evidence is collected as to the nature of these fossils, the interests of science will be best promoted by allowing the question to remain sub judice, and restricting the term Ventriculites to those zoophytes which possess the general characters of the type to which the name was originally assigned; namely, a vasiform or subcylindrical framework, terminating at the base in a point, and fixed by radicle processes; the substance consisting of a plexiform fibrous tissue; externally constituting a reticulated integument, the meshes disposed in a radiating manner from the base to the periphery; the inner surface studded with open cells regularly arranged.

In the former edition of this work the Ventriculites were placed with the Polypifera from the structure of the openings or cells, for these are so symmetrical, and disposed with so much regularity, as to present a closer analogy to the polype-cells of a coral, than to the large pores of a sponge. The doubts expressed by many eminent observers as to the correctness of this view, have induced me to insert this notice in the present section; leaving the true affinities of these organisms to be determined by future observers. Possibly we have in these fossils the relics of a tribe of zoophytes of an extinct type, that formed a connecting link between the _porifera_ and the _polypifera_; however this may be, I will venture to affirm that no one who had seen the infinitely varied examples of these fossils that I have, would for a moment confound them, as some naturalists have done, with the Scyphiæ, and other simple amorphozoa.

A Coral-polype in flint.

× 500 _diameters_.

(_Seen by transmitted light._)]

Polype in Flint. _Lign. 84._--I will here notice an exceedingly minute and interesting object, discovered by the Rev. J. B. Reade, in a flint containing vestiges of a Ventriculite, and which may possibly belong to this tribe of zoophytes. It must however be remarked, that there was nothing to show the collocation was not accidental. The drawing with which Mr. Reade favoured me, is engraved _Lign. 84_. This object is unmistakeably a polype-cell, with some of the integument of the animal protruding, in the form of a shrivelled tube. The possibility of soft animal tissues being preserved in flint, will not now admit of question, as we shall show when treating of the Foraminifera. The record of this fact may load to the discovery of other fossils of a like nature.

Fossil Polypifera.

[Sidenote: POLYPIFERA.]

As we proceed in our investigations, the impossibility of rigidly adhering to a zoological classification based on the structure of organs, of which but few, if any, traces exist in the mineral kingdom, becomes more and more apparent; the durable skeletons or polyparia being the only materials from which the palæontologist can gather information, relating to the physiology of the extinct coral-animals which swarmed in the ancient seas, and whose petrified remains constitute a large proportion of the secondary and palæozoic calcareous rocks.

Numerous fossil genera have been established by various authors from the external form of the polyparium, or the disposition and structure of the cells; but a slight attention to this department of palæontology will disclose corals which differ essentially from the typical forms, and new genera and species will require to be added to the already extended catalogue. The few genera selected for the present work, will convey a general idea of the nature of this class of fossils. To ascertain the names of the species he may collect, the student must refer to works especially devoted to the illustration of the corals of particular rocks; as for example, those of the British _Cretaceous_ deposits in the monographs of the Palæontological Society; of the _Palæozoic_ in _Sil. Syst._; and in Prof Sedgwick's Synopsis of the Classification of the Brit. Pal. Foss.; of the _Mountain Limestone_ in Prof, Phillips's work; and those of Ireland in Col. Portlock's Geological Memoirs. Those of the palæozoic rocks of New York, are illustrated in Prof. James Hall's splendid work on the Geology of that State.

The fossil zoophytes included in this section present innumerable varieties of form and structure, but agree in the important character of having originated, (with but few exceptions,) from aggregations of those minute beings termed Polypes (many-feet[229]). The common Hydra (_Wond._ p. 600), or fresh-water polype, that inhabits pools and streams, is a familiar example of a free animal of this kind, consisting of a cellular gelatinous substance, in the form of a short tube, or pouch, surrounded at the upper margin by long tentacula, or feelers, which appear to the naked eye as delicate threads. The _Polypifera_, properly so called, are groups of polypes, permanently united by a common integument or axis, each animalcule having an independent existence. A common support or endo-skeleton, termed _polyparium_,[230] is secreted by the integuments, which varies in its nature from a mere gelatinous, or horny material, to an earthy, calcareous, and even siliceous substance, that remains when the polypes die, and their soft parts have perished. All the varieties of corals, &c. are nothing more than the durable structures of aggregated masses of such beings.

[229] A name derived from the tentacula, or processes, which in some species serve for prehension, and in others for respiration.

[230] The basis, framework, or endo-skeleton, of these groups of animalcules is termed the _polyparium_, or _polypidom_ (polype-habitation); those of a stony hardness are familiarly known as corals; these names, therefore, refer to the durable substance, and not to the animals themselves; but in familiar writing, the term Coral is often used to designate the entire living mass. The Red-Coral forms a distinct genus called _Corallium_. In fossils, the _polyparium_ alone remains, except in very rare instances.