Chapter 14

[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.

[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: (fromsilexandcartilago) siliceous spicula in a cartilaginous mass.

Grantia: calcareous spicula in a gelatinous mass.

FOSSIL SPONGES.

M. D'Orbigny seems to believe that with the exception of the hornyCliona, 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.

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, theHalichondria, 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 variousstates 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]Achilleumof 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 inLign.69,fig.2: the surface of this fossil was covered with a white gritty powder, made up of minute needle-shaped siliceous spicula.

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 roundedand 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.

Spongites lobatus(sp. Fleming) is figured Pict. Atlas, pl. xxxix. fig. 6.

Lign. 69. Coral, and Spongites.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 inLign. 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 namedBracholitesby 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.

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]SeeExcursions, in vol. ii.

Lign. 70. Fossil Zoophytes.Fig.1.—Lunulites radiatus.Preston Chalk-pits; view of the convex side. (Mr. Walter Mantell.)1a.—Front view;nat.1b.—Portion of the surface of fig. 1, magnified.2.—Scyphia intermedia;1/2nat.Faringdon.3.—Lithododendron sociale: the left-hand branch shows a vertical section at the upper part, displaying the internal structure;1/2nat.Mountain Limestone, Yorkshire.4.—Verticillipora anastomosans.Faringdon.5.—Scyphia ramosa;1/2nat.Faringdon.6.—Scyphia foraminosa;1/2nat.Faringdon.7.—Cnemidium astrophorum;1/3nat.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, andLign. 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.

Lign. 71. Fossil Sponge;nat.(Chenendopora fungiformis.)Greensand. Faringdon.

Chenendopora.[206]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.

[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.

Lign. 72. Fossil Zoophytes;nat.Greensand. Faringdon.Fig.1.—Tragos peziza.2.—ProbablyChenendoporain a young state.3.—Verticillipora anastomosans.4.—Species ofScyphia.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 byfig.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 asT. Faringdoniensis.

The base in all these Greensand sponges is flat andexpanded; 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.

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 aSiphonia closely resembling this species; and varied sections of its stems produce the white markings commonly observable on the slabs of pavements.

Lign. 73. Siphoniæ, from the Greensand;nat.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 ofS. pyriformisin 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 severalforms that are allied in structure to the Siphoniæ. These fossils present considerable diversity of shape; one of the lobed forms is delineated inLign. 73, fig. 4: and a branched species inLign. 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."

Lign. 74.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.

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 (chieflyS. 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.

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 ofbundles 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 inLign. 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 termedpetrified 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 anActinia, orSea-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.

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

[214]From the supposition that the original was anActinia, orSea-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.

Lign. 75. Choanites Königi. (G. A. M.)Chalk, Lewes.Fig.1.—Transverse section of a siliceous specimen.2.—Upper portion of aChoanite, in chalk, showing the opening of the central cavity ata.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 ofSpiculaof 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. Iffig. 2, were placed on the top offig. 4, the general shape of the original zoophyte would be represented. The opening at the base offig. 4, marks the spot whence the processes of attachment proceeded. The vertical section of a flint, similar tofig.4, is shown atfig. 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 infig. 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 theActinia, strengthened by spicula; for numerous tri-radiate spines, like those on the left-hand offig. 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 thecentral 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; seeLign. 80, fig. 1.

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 appearancein situ, is representedLign. 76, from Dr. Buckland's illustrations:b, is a single specimen, partly imbedded in the chalk, andc,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 inthe 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.

Lign. 76. "Paramoudra;" seen in a vertical section of a Chalk-pit, near Moira.(The Very Rev. Dr. Buckland.Geol. Trans, vol. iv.)a, a, a.Layers of flint nodules, alternating with chalk strata,b.AParamoudra, 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 ofSteganodictyum.[215]

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

Clionites(Morris)Lign.130.—A recent parasitical sponge (first described by Dr. Grant under the name ofCliona), 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 nameClionites, to indicate their origin; they are not, however, the silicified sponge, but inorganic casts, moulded in the excavations. The common species isC. 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.

[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 inLign. 75. As theActinia,Gorgonia, andAlcyonia, possess spicula, some of the fossil spines may have been derived from those zoophytes. The larger spicules may bediscovered 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.

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