Chapter 31

[461]Geol. Trans. 2d ser. vol. v. pl. xlvii.[462]On account of the distinctive characters of their carapace-valves, M. Bosquet has suggested the appellationCyprideaas a generic name for the Cyprididæ of the Wealden and Purbeck beds.

[461]Geol. Trans. 2d ser. vol. v. pl. xlvii.

[462]On account of the distinctive characters of their carapace-valves, M. Bosquet has suggested the appellationCyprideaas a generic name for the Cyprididæ of the Wealden and Purbeck beds.

The appearance of four characteristic Wealden Cyprides, of their natural size and magnified, is shown inLign.174. The one namedC. Valdensis, or Wealden Cypris, by Dr. Fitton and Mr. Sowerby (fig. 1), is the most frequent, and occurs in numerous localities in Kent and Sussex. A Cypris having the case studded with relatively large tubercles(fig. 3), is found in many of the finer sandstones of Tilgate forest; another, with the shell tuberculated, but divided by a transverse ridge (fig. 2), indicating a rudimentary condition of the segments which characterise the class, is certainly distinct from the former, and can have no name more appropriate than that ofC. Fittoni. The other beautiful species (C. granulosa, fig. 4) has the surface of the case covered with granules. One more species has been observed in the Weald clay, at Sandown Bay and Atherfield (by Mr. Lonsdale); it is distinguished by a short conical spine on each valve, and is therefore namedC. spinigera. In the Weald clay at Resting-oak-hill, near Cooksbridge (Geol. S. E.p. 187),C. Valdensisis so abundant, that every thin flake is covered with its white calcareous shells; and upon breaking the nodules and septaria of reddish-brown ironstone which occur in that locality, myriads of beautiful sharp casts of the cases are observable in almost every fragment. They are associated with fresh-water bivalves and univalves (CyclasandPaludina), and minute scales of fishes. The sandstone at Langton Green, near Tunbridge Wells, which contains casts and impressions of several species of fresh-water shells, abounds inCyprides; and the layers of argillaceous ironstone, interstratified with the sandstone in one of the quarries, are particularly rich in these remains. The surface of a recently broken slab is often covered by minute, polished, oblong, convex bodies, which are the casts of cypridean carapaces.

The Sussex marble is largely composed of the remains of these minute crustaceans. Upon examining thin polished slices of this limestone under the microscope, the cavities and interstices of the shells are found to be filled with the shields of Cyprides, entire or in fragments; and some specimens of the Purbeck marble equally abound in these remains. The Purbeck marls, as well as the limestones, often abound with Cyprides. According to Prof. E. Forbes, thesebelong to several species, all more or less distinct from those of the Wealden (Brit. Association, 1850). The Cyprides of the Wealden of Germany have been figured and described by Dr. Dunker; and several of the British forms are found there.

As the recent species inhabit still lakes, or gently running streams, and not the turbulent waters of estuaries, we cannot doubt that the strata in which these animals so largely predominate were deposited in lakes or bays, communicating with the river which transported to their present situation the bones and other remains of the colossal reptiles of the Wealden. And the beds of fresh-water snails, with scarcely any intermixture of other organic remains but the Cyprides, which are spread over extensive areas in the Wealden and Purbeck districts, appear to afford corroborative proof of this inference.

Four species of minute bivalved Entomostraca from the Carboniferous deposits have been referred toCypris: viz.C. arcuata, Bean, from the Coal-shale at Newcastle;C. inflata, Murchison, Coal-measures, near Shrewsbury;C. Scoto-Burdigalensis, Hibbert, Coal-measures at Burdie-house, and Coal-shale at Derry; andC. subrecta, Portlock, also from Derry, Tyrone.

Cythere.[463]—This animal differs but little from Cypris except in having an additional pair of feet. In the SubgenusCythereisthe valves are thick, oblong, and strongly hinged; thus differing from the thin and more or less oval valves of the true Cythere and of Cypris. Several species ofCythereand its sub-genera occur in the Tertiary, Cretaceous, Oolitic, Liassic, Permian, and Carboniferous deposits.[464]

[463]For description and illustration of this genus, see Baird’s British Entomostraca, p. 163, &c.[464]Consult M. Bosquet’s Memoir on the Tertiary Entomostraca of Belgium and France; Mr. T. R. Jones’s Monograph of the Cretaceous Entomostraca (Palæontographical Society), and of the Permian Entomostraca, in Prof. King’s Monograph of the Permian Fossils (Palæont. Soc.); and Prof. M’Coy’s Synopsis of the Characters of the Mountain Limestone Fossils of Ireland.

[463]For description and illustration of this genus, see Baird’s British Entomostraca, p. 163, &c.

[464]Consult M. Bosquet’s Memoir on the Tertiary Entomostraca of Belgium and France; Mr. T. R. Jones’s Monograph of the Cretaceous Entomostraca (Palæontographical Society), and of the Permian Entomostraca, in Prof. King’s Monograph of the Permian Fossils (Palæont. Soc.); and Prof. M’Coy’s Synopsis of the Characters of the Mountain Limestone Fossils of Ireland.

Three species of Entomostraca, very closely related toCypridina,[465]from the Carboniferous rocks of Belgium, hare been figured and described by M. De Koninck; one species from the Carboniferous rocks of Ireland, by Prof. M’Coy;[466]and two species from the Cretaceous limestone of Maestricht,[467]by M. Bosquet. The generaCyprellaandCypridellahave been established by M. De Koninck for the reception of some allied forms found in the Carboniferous strata of Belgium; and Entomoconchus (M‘Coy) andDaphnoidia(Hibbert) are allied British Carboniferous forms.

[465]See Baird’s British Entomostraca, p. 176, &c.[466]Under the name ofDaphnia primæva.[467]Under the generic appellation ofCyprella.

[465]See Baird’s British Entomostraca, p. 176, &c.

[466]Under the name ofDaphnia primæva.

[467]Under the generic appellation ofCyprella.

Trilobites.—Among the numerous petrifactions which are found in the limestones in the neighbourhood of Dudley, in Staffordshire, there are certain fossil bodies which, from their extraordinary form and appearance, have for more than a hundred and fifty years been objects of great interest to the naturalist, and of wonder to the general observer, and have long been provincially termedDudley insects, orlocusts.[468]By the earlier naturalists these fossils were referred to fishes, to molluscs, and to insects, before their real character was discovered. The most common type consists of a convex, oblong body, divided transversely into three principal parts, and longitudinally into three lobes, by two deep, parallel furrows; this last character suggested the nameTrilobita, orTrilobites, by which the family is now distinguished by naturalists.

[468]Lhywd.Philos. Trans. for the year 1698.

Lign. 175. Trilobites.Silurian Limestones.Fig.1.—Illænus perovalis.(Murch. Sil. Syst.)2.—Trinucleus Lloydii.(Murch. Sil. Syst.)3.—Calymene Blumenbachii: the upper surface of the carapace, viewed from above.Dudley.4.—The same, coiled up, and seen in profile.4a.—The same, seen in front.

These fossils are the carapaces, or shells, of crustaceans, belonging to an extinct family,[469]which comprises many genera, and numerous species. Mortimer, Da Costa, Guettard, and Linnæus recognised the crustacean character of this interesting, but obscure class of organic remains: their true affinities, however, were first scientifically determined by Alex. Brongniart.[470]Many memoirs on theTrilobiteshave since been published by eminent Continental and American writers;[471]and much light has been thrown on the subject by the labours of Martin,[472]Parkinson,[473]Stokes, Phillips,[474]König,[475]Dr. Buckland,[476]Sir E. I. Murchison,[477]and others. The beautiful illustrations and interesting description of the Trilobites in Dr. Buckland’s Bridgewater Treatise (Bd.p. 389, and pl. xlv. xlvi.) must have rendered the reader familiar with the most important facts relating to these extinct beings; but subsequent discoveries have thrown additional light on their structure and natural affinities. The works of M. Burmeister,[478]Mr. Salter,[479]Prof M’Coy[480]and especially of M. Barrande,[481]should be carefully referred to by the student in this branch of Palæontology.

[469]The Trilobites appear to have been related more nearly to the Phyllopoda than to any other division of the Crustacea.[470]Hist. Nat. Crust. Foss. Burmeister on Trilobites; Introduction.[471]A Monograph on the Trilobites of North America, by Jacob Green, M.D. Philadelphia, 1832.[472]Petrificata Derbiensia.[473]Organic Remains of a Former World, vol. iii. See Pictorial Atlas.[474]Geology of Yorkshire; and Palæozoic Fossils of Devon.[475]Icones Fossilium Sectiles.[476]Bridgewater Treatise.[477]Silurian System, chap, xlvii.[478]Die Organisation der Trilobiten. 1843. Translation: Ray Society.[479]In the Quarterly Journal of the Geological Society, and in the Memoirs and Decades of the Geological Survey of Great Britain.[480]Palæozoic Fossils in the Cambridge Museum.[481]The Silurian System of Bohemia: the Trilobites.

[469]The Trilobites appear to have been related more nearly to the Phyllopoda than to any other division of the Crustacea.

[470]Hist. Nat. Crust. Foss. Burmeister on Trilobites; Introduction.

[471]A Monograph on the Trilobites of North America, by Jacob Green, M.D. Philadelphia, 1832.

[472]Petrificata Derbiensia.

[473]Organic Remains of a Former World, vol. iii. See Pictorial Atlas.

[474]Geology of Yorkshire; and Palæozoic Fossils of Devon.

[475]Icones Fossilium Sectiles.

[476]Bridgewater Treatise.

[477]Silurian System, chap, xlvii.

[478]Die Organisation der Trilobiten. 1843. Translation: Ray Society.

[479]In the Quarterly Journal of the Geological Society, and in the Memoirs and Decades of the Geological Survey of Great Britain.

[480]Palæozoic Fossils in the Cambridge Museum.

[481]The Silurian System of Bohemia: the Trilobites.

In the Trilobites the head is distinct, and without antennæ, and the feet are supposed to have been rudimentary, soft, and membranaceous: the essential characters which separate them from all other crustaceans, exceptBopyrus(a parasite on the branchiæ of the common prawn), are, according to Mr. Macleay, the deficiency of antennæ, and of lateral posterior abdominal appendages, and the presence of evanescent feet. Like other crustaceans, the Trilobites were subject to the process of metamorphosis during their early stages of life; and M. Barrande has ascertained that one species, theSaö hirsuta, appeal’s in no less than twenty different stages of development. In its earliest, embryonic condition, it is a simple disk, and it passes through various stages until it becomes a perfect adult trilobite, having seventeen free thoracic segments and two caudal joints. No less than ten genera and eighteen species were institutedby palæontologists onsomeof the forms only which this one species presents in its different stages of metamorphosis, before M. Barrande’s laborious and long-continued investigations gave him an insight into the true relations of these various conditions of the same animal to one another. This talented and indefatigable palæontologist has arrived at like results with other Trilobites, and has been enabled to add greatly to our knowledge of the natural history and geological distribution of this interesting group of crustaceans. See Transact, of the Sections, Brit. Assoc. 1849 and 1850; andTrilob. Bohême, pl. vii.

TheTrilobiteshave been arranged in numerous genera, the names of which in a few cases are expressive of natural characters, but in others have reference to the obscurity that still invests some parts of the organization of these animals.[482]

[482]As, for example, Asaphus,obscure; Calymene,concealed; Agnostus,unknown.

Calymene Blumenbachii.Lign.175,figs.3, 4.—This is the Trilobite so well known as the Dudley locust, or insect. It consists of an ovate, convex, trilobed crustaceous shell, or case, and is found either expanded, as inLign.175,fig.3, with its under surface attached to, and blended with, the limestone (Wond.p. 789); or coiled up like an Oniscus, or wood-louse, as infigs.4 and 4a. The head is large, convex, rounded in front, with a broad border, and divided into three lobes by two longitudinal depressions. The eyes are two in number, compound, and have numerous facets; they are situated on the sides of the head, remote from each other. The carapace is deeply trilobed by two longitudinal furrows; the thoracic portion is composed of thirteen segments; the caudal shield is small and nearly semicircular. This species is from one to four inches in length. It occurs from the Lower Llandeilo rocks up to the Upper Ludlow inclusive.

The structure here described may be regarded as the normal type, but numerous and important modifications prevail in the different genera.

Lign. 176 Homalonotus dephinocephalus.(Reduced frompl. vii.Sil. Syst.)Upper Silurian.Dudley.

In the genusHomalonotus,Lign.176, the thoracic portion of the carapace is but obscurely lobed, and consists of thirteen segments; the abdominal is distinct from the thoracic, and formed of nine rings; it terminates in a prolonged point. TheH. Herscheliiis a large Trilobite, very plentiful in the Upper Silurian schists of the Cape of Good Hope.

In another genus,Asaphus(Geol. Surv. Decade 2), the carapace is wide and much depressed; the middle lobe distinct, the cephalic portion rounded in front, and terminating posteriorly in a sharp process on each side. The eyes are compound, and each contains upward of six thousand lenses, many of which remain in some examples.[483]Some American species belonging to this group are of a gigantic size, as, for example, theIsotelus gigas(of Mr. Dekay), which iseighteen inches long. In theIsotelus[484]the body is of an oval shape, and the posterior angles of the head are rounded; the thorax is composed of eight segments.

[483]Mem. Geol. Surv. Decade 2, pl. v. p. 2, note.[484]Isotelus, i. e. equal extremities.

[483]Mem. Geol. Surv. Decade 2, pl. v. p. 2, note.

[484]Isotelus, i. e. equal extremities.

Another division of the Trilobites has the body contracted, and very thick, and the abdomen large and scutiform, without any segmentary divisions; the small crustacean (Illænus perovalis,Murch.)Lign.175,fig.1, will serve to illustrate these characters.

The Trilobite calledBumastusby Sir R. Murchison (from its grape-like form) presents a very curious modification of the normal type. Both the head and caudal extremity are rounded, with no distinct longitudinal furrows; and the whole surface of the carapace is covered by extremely thin, apparently imbricated, lamellæ, the edges of which are undulated, and the intermediate spaces studded with minute dots. The eyes are smooth, and not granulose, as in Calymene. This genus is known in England by the name of theBarr Trilobite, from its occurrence in the limestone near Barr, in Staffordshire; it is sometimes five inches long, and three and a half wide (Geol. Surv. Decade 2, pl. iii. and iv.).

The genusOgygia(Bd.pl. xlvi. fig. 9) is characterised by the elliptical and depressed form of the carapace, its nearly balanced extremities, and the prolongation of the buckler, or cephalic portion, on each side, into slender spikes, distinct from the body; the thoracic and abdominal regions are divided by two deep, longitudinal furrows, into three lobes; there is also a straight, longitudinal groove, in the front of the buckler (see figures and descriptions ofO. Buchii,Geol. Surv. Decade 2). The Trilobites of this genus are found in the Lower Silurian rocks of North Wales and Ireland; they occur also in great abundance in the slate rocks of Angers, and some species are more than a foot in length.

Some species of the genusPhacopshave long, pointed caudal appendages, as theP.(formerlyAsaphus)caudatus(Lign.177;Bd.pl. xlv. figs. 10, 10′; andGeol. Surv. Decade 2, pl. i.). The eyes are often well preserved, and each contains about 240 spherical lenses.

Lign. 177. Phacops caudatus.Upper Silurian.Dudley.The caudal extremity.

Trinucleus.Lign.175,fig.2;Ly.fig. 432.—This genus comprises several small forms which are found in the Lower Silurian rocks of England, and occur in the equivalent deposits of Sweden, Norway, and Russia.[485]In theTrinucleus, the cephalic shield is obtuse, trilobed, rounded, and terminating in lateral spikes; and its margin is marked by numerous pit-like depressions. There are six body-rings or thoracic segments. The caudal shield is large and somewhat triangular. There are no distinct eyes.

[485]Murch. Sil. Syst. p. 217.

Paradoxides.Lign.178.—The Trilobites of this genus are easily recognised by the ends of the lateral segments of the thorax and abdomen terminating in deflected points, which extend in spikes beyond the membrane they supported, and particularly those near the tail, which are much elongated; whereas in the other genera the lateral points of the segments are united by a membrane, which often forms a border beyond them. The cephalic buckler is semicircular, and its lateral angles are lengthened outbehind into two strong spines; it is divided on the median line into four protuberances, by transverse grooves. The thorax consists of from sixteen to twenty segments; the abdominal buckler is generally very small and rounded. The animals of this genus have the body much depressed, and the lateral lobes wider than the middle lobe: some species are of considerable size, attaining several inches in length.

Lign. 178. Paradoxides Bohemicus:nat.Silurian.Bohemia.

A very peculiar form of Trilobite (Brontes flabellifer,Ly.p. 348) is found in the Devonian strata of the Eifel and South Devonshire; the head, or cephalic region, is narrow, and has two lunated eyes; the thoracic region is trilobed and short, and composed of about ten small articulations; the abdominal very small, and bordered by segments, which radiate and form a wide, fan-shaped expansion. Other species of this genus occur in the Silurian rocks.

With regard to the under surface of the Trilobites much remains to be known. No decided indications either of antennæ or extremities have been discovered. In an American specimen, Mr. Stokes detected a plate,[486]which appearsto be alabrum, or upper mandible or lip, resembling that ofApus cancriformis. This animal has a similar labrum, "and lateral influted terminations of the shelly segments of the body, with a distinctly trilobedpygidium(tail or caudal portion), and a prolonged tail: the feet being foliaceous, and the abdomen merely covered by a membrane."[487]In the upper or dorsal surface of the carapace the Trilobites approach certainIsopoda, particularly in the characters of the buckler and eyes. Mr. Macleay states that among the existing crustaceans there are certain genera which individually possess some one or more of the characters, which have been thought peculiar to the extinct Trilobites. Thus theSerolis(Bd.pl. xlv. fig. 6), and theBopyrus, have a trilobed form; the femaleCymothoæhave the coriaceous margin of the body, and in some species are without eyes as are many of the Trilobites; while the eyes of the males of someCymothoæare composed of large facets, and are situated on the back of the head, wide apart, as in theCalymene; rudimentary feet, and the absence of antennæ occur inBopyrus; and lastly, theSphæromahas an onisciform body, and the power of rolling itself up into a ball, like the Calymene (Lign.175,fig.4). The analogy between the Bopyrus and the Barr Trilobite is so close, that if the latter had a body with thirteen equal segments, and short crustaceous feet, it would be in every essential particular a maleBopyrus.[488]Burmeister regards the Trilobites as being related to theBranchipus. From the absence of eyes in the female, and their presence in the male of certain recent genera of crustaceans, it is not improbable that a similar character may have prevailed in the Trilobites, and that certain fossils referred to different genera, from the presence or absence of eyes, may have been the males and females of the same species.

[486]Geol. Trans, vol. ii. p. 208. See alsoBd.pl. xlv,fig.12; and Burmeister, pl. vi.[487]Murch. Sil. Syst. p. 665.[488]Ibid. p. 667.

[486]Geol. Trans, vol. ii. p. 208. See alsoBd.pl. xlv,fig.12; and Burmeister, pl. vi.

[487]Murch. Sil. Syst. p. 665.

[488]Ibid. p. 667.

The habits of the Trilobites, as deducible from Mr. Macleay’s exposition of their structure and affinities, must have resembled those of theCymothoadæ, some of which, like the Calymenes, coil themselves up, and are not parasitical; while their close affinity to Bopyrus, and the apparent absence of distinct crustaceous feet, imply that they were to a certain degree sedentary. The flat under surface of their bodies, and the lateral coriaceous margin of several species, which is so analogous to that of the multivalve shellChiton, render it probable that they adhered by a soft, articulated, under surface, to the rocks or sea-weeds. Their instruments of progression are unknown; whether they moved by means of membranaceous feet, or by the undulations of setigerous segments, like the earth-worm, or by wrinkling the under surface of the abdomen, like the Chiton, are questions yet to be determined. It is evident, from their longitudinally trilobed form, and lateral coriaceous margin, that they had the power of firmly adhering to flat surfaces; and while thus sedentary the thin but hard dorsal crustaceous shell would protect them from the attacks of their enemies. "The Trilobites, probably, like the Chitones, adhered in masses one upon another, and thus formed those conglomerations of individuals which are so remarkable in certain rocks; but it is not likely that they were parasitical, since almost all the existing parasites that adhere to other animals, have strong feet, armed at their extremities with hooks for that purpose."[489]From the form of thelabrumof the mouth (Barrande, pl. i. and ii A) it is inferred that they were carnivorous, preying on naked mollusks, or on the annelides, with which their remains are associated.

[489]Murch. Sil. Syst. p. 669.

As the compound eyes of theTrilobites[490]are similar tothose of existing crustaceans and insects (seeWond.p. 792), the highly interesting and important fact is established, that the mutual relations of light to the eye, and of the eye to light, were the same in the remote epoch when the Trilobites flourished, as at the present time; and that the condition of the waters of the sea, and the atmosphere, and the relation of both these media to light, have undergone no change through the countless ages that have elapsed since the deposition of the Silurian strata.[491]

[490]The compound eyes in many specimens remain in a high state of preservation. M. Barrande in the eye of aBrontes palifercounted 30,000 lenses. See also Barrande, pl. iii.[491]See Dr. Buckland’s eloquent and instructive commentary on this subject,Bd.pp. 401-404.

[490]The compound eyes in many specimens remain in a high state of preservation. M. Barrande in the eye of aBrontes palifercounted 30,000 lenses. See also Barrande, pl. iii.

[491]See Dr. Buckland’s eloquent and instructive commentary on this subject,Bd.pp. 401-404.

Geological Distribution of Fossil Crustaceans.We have seen that the Tertiary strata contain the remains of many of the highest organized crustaceans; a few brachyurous, macrurous, and entomostracous genera appear in the Cretaceous, Oolitic, and Liassic formations; whilst the IsopodousArchæoniscusand several species of Cypris occur in the Wealden and Purbeck deposits. Some few Entomostraca have been enumerated from the Trias and Permian.

One species of macrurous decapod has been found in the Muschelkalk of Germany; and Mr. Prestwich’s "Apus dubius" (Geol. Trans.2d ser. vol. v. pl. xli.fig.9), and Dr. Ick’s crustacean, noticed inJourn. Geol. Soc.vol. i. p. 199, both from the Coal Measures of England, are probably true Decapodous Crustaceans. With these exceptions not a species of the numerous tribes of Crabs, Lobsters, &c. has been observed in the older formations, though composed of such enormous thicknesses of marine detritus, and containing countless myriads of the relics of the inhabitants of the ocean.

A few species ofLimulus, severalCytheresand allied genera, and a few Trilobites (PhillipsiaandGriffithides)belong to the strata of the Carboniferous System. In the Devonian System we find some minute entomostracans, the giganticPterygotus, and various Trilobites (Brontes,Cheirurus,Homalonotus,Phacops, &c.); but it is the Silurian rocks that constitute the grand mausoleum of those ancient beings, the Trilobites.

There are about thirty genera of Trilobites found in the Silurian rocks of Great Britain and Ireland. Many of these are common to the Upper and Lower Divisions of that system; and some of them are met with both in the Silurian and in the Devonian rocks, asPhacops,Brontes,Cheirurus,Harpes, andHomalonotus. TheCalymene Blumenbachii(Lign.175,figs.3 and 4) ranges through the Ludlow and Wenlock, to the Bala and Llandeilo formations. ThePhacops caudatusalso (Lign.177), theCheirurus bimucronatus,[492]and theEncrinurus punctatus[493]extend from the Ludlow, to the Llandeilo formation. The Upper Silurian rocks exclusively contain some peculiar forms, asEncrinurus variolaris,Bumastus Barriensis, and several species ofAcidaspis. And the Lower Silurian has several distinct genera, namely, theTrinucleus(Lign.175,fig.2),Ogygia,Agnostus,Asaphus,Olenus,Remopleurides, &c. One species ofPterygotus, and one ofEurypterus, theCeratiocarisandHymenocaris, and several species of the minute bivalved Entomostraca (LeperditiaandBeyrichia) are all that remain to be enumerated as constituting, in company with theTrilobites, the Crustacean fauna of the ancient Cambrian and Silurian seas.[494]

[492]In Murchison’s Silurian System this form is figured (pl. xiv. figs. 8 and 9) and described as Paradoxides bimucronatus.[493]This is described and figured as Asaphus tuberculatus in Buckland’s Bridgewater Treatise, pl. xlvi.fig.6.[494]We have also to refer to the indications of the existence of other large Silurian Entomostraca afforded by the magnificent series of fossil foot-tracks lately brought to England by W. E. Logan, Esq., and obtained by that gentleman from the Potsdam Sandstone (Lower Silurian) of Eastern Canada. These foot-marks and trails have been determined by Prof. Owen as being most probably referable to some large Crustaceans of theLimulusGroup, and are named by himProtichnites. (See drawings and descriptions in the Quarterly Journal of the Geological Society, vol. viii.)

[492]In Murchison’s Silurian System this form is figured (pl. xiv. figs. 8 and 9) and described as Paradoxides bimucronatus.

[493]This is described and figured as Asaphus tuberculatus in Buckland’s Bridgewater Treatise, pl. xlvi.fig.6.

[494]We have also to refer to the indications of the existence of other large Silurian Entomostraca afforded by the magnificent series of fossil foot-tracks lately brought to England by W. E. Logan, Esq., and obtained by that gentleman from the Potsdam Sandstone (Lower Silurian) of Eastern Canada. These foot-marks and trails have been determined by Prof. Owen as being most probably referable to some large Crustaceans of theLimulusGroup, and are named by himProtichnites. (See drawings and descriptions in the Quarterly Journal of the Geological Society, vol. viii.)

On Collecting Fossil Crustaceans.—The Crabs and Lobsters of the argillaceous tertiary strata are generally imbedded in nodules of indurated clay and septaria. On the shore beneath the cliffs on the north of the Isle of Sheppey, and near Southend, specimens may be observed in the nodules that have been exposed to the action of the waves, the attrition to which they have been subjected having partially worn away the surrounding stone, and displayed the enclosed fossils. In these examples the carapace is occasionally seen on one side, and the pair of pincer-claws on the other face of the boulder; the other feet and the plates of the thorax may sometimes be developed in such examples by chiselling away the enveloping mass. In the laminated marls of the tertiary and other deposits, in which the minute crustaceans, as theCypridesabound, thin slabs covered with these relics may be easily extracted; and many of the tertiary clays and sands yieldCytheres, together withForaminiferaand other minute fossils, on careful washing and examination with a lens.

The Chalk crustaceans, particularly those which are muricated, or beset with spines and tubercles, as theEnoploclytia SussexiensisandE. Leachii(Lign.169), require considerable patience and dexterity to develope successfully. The crustaceous covering of the carapace and claws adheres firmly to the chalk by the rough external coat, while the inner, smooth, glossy surface as readily separates. Hence, upon breaking a block of chalk containing portions of these crustaceans, we find one piece exhibiting a chalk cast of the claw or carapace, covered with tubercles or papillæ, that have been moulded in the bases of the spines of the crust;and on the other portion the crustaceous shell imbedded by its outer surface, and presenting the internal glossy lining, beset with circular depressions, which are the bases of the spines. This crust is exceedingly friable, and will flake off by a very slight touch. To obtain specimens with the external characters, it is necessary to proceed with great caution; and when indications of a crustacean are observed in a block, the chalk should be chiselled or sawn off to within half an inch of the surface of the fossil, and the remainder of the stone be cleared away, piece by piece, by means of a penknife or graver. By this process the fossils figuredFoss. South D.pl. xxix. xxx. xxxi. were developed. When a fine specimen has been broken, and the shell is attached to one piece of the stone and the cast to the other, it is possible to obtain an illustrative example of the external surface, by cementing the pieces accurately together with very thin hot glue; and, when firmly consolidated, the chalk may be removed, and the spines, tubercles, and papillæ of the crustaceous covering be developed by the method previously described. A thin coating of mastic varnish will give durability to the crust, and improve its appearance; but the rich brown colour it possesses when first exposed soon disappears. The Crustaceans of the Galt are often found amongst the argillaceous and pyritous nodules flung aside in heaps where the Galt is used for brick-making.

TheCytheridæof the Chalk, Galt, Oolite, &c. are to be obtained by disintegrating the matrix in water, and examining the debris, after sifting, under a lens.

The Limuli of the Coal-measures often form the nuclei of clay nodules, as in the example figuredLign.172, in whichfig.2 represents the nodule without any external indication of its contents, andfigs.1, and 3, the same broken, and displaying the crustacean. Traces of the legs, branchiæ, and other appendages, should be diligently sought for in fossils of this kind, for they are more likely to be detected in suchspecimens than in those found in limestone. It is possible that polished sections of the coiled up examples of Trilobites (Lign.175,fig.4) would throw some light upon the nature of the hitherto undiscovered organs of locomotion and respiration of this extinct order of Crustaceans.

A FEW BRITISH LOCALITIES OF FOSSIL CRUSTACEANS.

Abberley. Silurian:TrilobitesandBeyrichia.

Aberystwith, neighbourhood of. Silurian:Trilobites.

Arundel, Sussex. Chalk-pits in the vicinity. Astacidæ and Cytheridæ.

Atherfield, Isle of Wight. Wealden:Cypridesin clay (Lign.174).

Barr, Staffordshire; limeworks at Hay Head. Silurian:Trilobites, particularly of the genusBumastus.

Bewdley, Shropshire. Silurian:Trilobites.

Bolland, Yorkshire. Carboniferous Limestone:Trilobites(Cyclus,Phillipsia).

Burdie-house, near Edinburgh. Fresh-water coal-measures.CypridesandEurypteri.

Burham, near the banks of the Medway, Kent. Quarry of Mr. W. Lee, a good section of the lower Chalk: fineCrustaceans.

Coalbrook Dale. Coal-measures and Silurian.LimuliandTrilobites.

Coniston, Lancashire. Silurian:Trilobites.

Dinley, Wilts. Purbeck.Isopoda(Lign.171) andCyprides.

Dover. In the lower Chalk,Astacus(Enoploclytia)Sussexiensis, &c.

Dudley. Upper Silurian:Trilobitesin abundance.

Durlstone Bay, near Swanage. Purbeck:CypridesandIsopoda.

Folkstone, Kent. In Galt: small Crabs (Lign.168), and numerousCytheres.

Grays, Essex. Pleistocene:Cyprides.

Gristhorpe Bay, Yorkshire Oolite:Astacidæ.

Hastings, Sussex, neighbourhood of. Wealden:Cyprides.

Hollington, near Hastings. Wealden:Cyprides.

Hordwell Cliff, Hampshire. Upper Eocene:Cyprides.

Kildare, Ireland. Carboniferous and Silurian:Trilobites.

Langton Green, near Tunbridge Wells. Wealden:Cyprides.

Lewes, Sussex. In the Chalk-pits of the vicinity: Astacidæ (Lign.169), and other Crustaceans.

Llandeilo, Caermarthenshire. Lower Silurian:Trilobites,Trinuclei.

Lyme Regis, Dorset. Green Sand: Hoploparia. Lias:Coleia.

Malvern Hills. Lower Silurian.Trilobites(Olenus).

Meifod Hills, Montgomeryshire. Silurian:Trilobites.

Mount Pleasant, Caermarthen. Silurian:Trilobites.

Newton Bushel. Devonian:Trilobites(Brontes).

Rhiwlas, near Bala, North Wales. Lower Silurian:Trilobites.

Ringmer, near Lewes. In Galt: smallCrabs, &c.

Sandown Bay, Isle of Wight.Cyprides, in Weald Clay.

Scarborough. Oolite:Astacidæ, in clay nodules.

Sheppey. London Clay:LobstersandCrabs.

Steyning, Sussex. In Chalk-marl:Lobsters, &c.

Tyrone, Ireland. Carboniferous and Silurian:Trilobites.

Wenlock, neighbourhood of. Upper Silurian:Trilobites.

Westbury, Gloucestershire. Lias:EstheriaandCyprides.

Wilmington, near Marton, Salop. Silurian:Trilobites.

Wistanstow, Salop. Lower Silurian:Trilobites.

Worthing, Sussex. Neighbouring Chalk-pits.Lobsters, &c.

FOSSIL INSECTS, SCORPIONS, AND SPIDERS.

From the Crustaceans we pass by a natural transition to the other Articulata, viz. theArachnida(Scorpions and Spiders) and theInsecta, in the last of which "the highest problem of animal mechanics is solved, and the body and its appendages can be lifted from the ground and propelled through the air" (Owen). The skeleton in these animals, as in the Crustaceans, is chiefly external, and consists of a hard shell or case (composed of a peculiar substance, termedchitine), divided into segments, and furnished with articulated or jointed hollow extremities. The head is distinct, and has a pair of compound eyes, and of jointed antennæ. To the segments that form the thorax the legs are attached, and these consist of three pieces in the hexapods (insects with six feet), each supporting a pair of feet. The wings in the flying insects are attached to the middle and third thoracic segments. The legs, or articulated appendages, are hollow, as in the Crustaceans, and contain the muscles and other soft parts. The generic and other distinctionsadopted by naturalists, to facilitate the study of this most numerous division of the animal kingdom, are founded on the structure and configuration of the antennæ and wings. The latter consist of flat membranous expansions, supported by hollow tubes or nervures; and in some orders consist of one pair, and in others of two. In burrowing insects, as the Beetle, the front pair of wings constitutes a hard case (elytron), which covers and protects the membranous posterior pair, when the animal is in repose or walking. The modifications of the wings furnish the characters by which the class is divided into orders. Thus theColeoptera(sheathed-wings) comprise the beetles and other burrowing insects, in which the membranous wings are folded transversely beneath the elytra, or wing-cases. TheOrthoptera(straight-wings), those with two pairs of wings, of which the anterior encase the others, the posterior being membranous, and folded longitudinal during repose; as the Earwig, Cockroach, Mantis, and Locusts.Neuroptera(nerved-wings), those with two pairs of transparent reticulated wings, as the Libellula, or Dragon-fly, the Ephemera, and the Termites.Hymenoptera(membranous-wings), with simply veined membranous wings, as the Gall-flies, the Bee, &c. The Cicas, Aphis, and Coccus constitute the somewhat anomalous group termedHomoptera(equal-wings), in which the anterior pair of wings are usually similar to the posterior in consistence, and shut up in a roof-like manner. TheHeteroptera(different-wings) include the Nepa, Notonecta, &c. and have the anterior wings coriaceous at the base, membranous towards the point, and shutting up nearly horizontally, partly lapping over one another.Lepidoptera(scaly-wings) have wings covered with scales, as the Butterfly and Moth. In theDiptera(two-wings) the anterior pair of wings only are the instruments for flying, and the hinder pair are reduced to mere clavate appendages, as the Gnat and Fly. The Phryganeæ(Caddis flies) constitute the order ofTrichoptera(hairy-wings), related to the Neuroptera, but resembling the Lepidoptera in the distribution of the nervures of the wings, and in many other characters. Lastly, there remain the Wingless Insects, divisible into three orders, of which the Flea, the Parasites, and the Podura are respectively the types. With these few remarks on those durable parts of the structure of Insects which their fossil remains generally present, we must quit this part of the subject, and enter upon the examination of the relics which are the immediate objects of our present inquiry.

From the enduring nature of the elytra, segments, and articulated extremities of insects, the fossil remains of animals of this class might naturally be expected to abound in lacustrine and fluviatile deposits; this, however, is not the case, and except in a few favoured localities, fossil insects are seldom met with, and good specimens rank among the most rare and interesting of the organic remains of the Secondary formations. In certain Tertiary beds, as at Œningen, and Aix in Provence, insects of numerous species and genera have been discovered; and the cream-coloured limestone of Solenhofen, among its numerous other treasures, has yielded some fine examples of this class. The strata in which remains of insects have been found in England[495]are the Tertiary clays of the Bagshot series, the Hastings beds, Purbeck marls and limestones, Kimmeridge Clay, Oxford Clay, Forest Marble, Stonesfield Slate, Upper and Lower Lias, and the Coal Measures.

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