Chapter XIII (2)

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, the _Isotelus gigas_ (of Mr. Dekay), which is eighteen inches long. In the Isotelus[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.

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 called Bumastus by 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 the Barr 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 genus Ogygia (_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 of _O. 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 genus Phacops have long, pointed caudal appendages, as the _P._ (formerly _Asaphus_) _caudatus_ (_Lign. 177_; _Bd._ pl. xlv. figs. 10, 10′; and _Geol. Surv. Decade 2_, pl. i.). The eyes are often well preserved, and each contains about 240 spherical lenses.

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 the _Trinucleus_, 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 out behind 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.

_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 appears to be a _labrum_, or upper mandible or lip, resembling that of _Apus cancriformis_. This animal has a similar labrum, "and lateral influted terminations of the shelly segments of the body, with a distinctly trilobed _pygidium_ (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 certain _Isopoda_, 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 the _Serolis_ (_Bd._ pl. xlv. fig. 6), and the _Bopyrus_, have a trilobed form; the female _Cymothoæ_ have 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 some _Cymothoæ_ are composed of large facets, and are situated on the back of the head, wide apart, as in the _Calymene_; rudimentary feet, and the absence of antennæ occur in _Bopyrus_; and lastly, the _Sphæroma_ has 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 male _Bopyrus_.[488] Burmeister regards the Trilobites as being related to the _Branchipus_. 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 also _Bd._ 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 the _Cymothoadæ_, 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 shell _Chiton_, 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 the _labrum_ of 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 the _Trilobites_[490] are similar to those of existing crustaceans and insects (see _Wond._ 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 a _Brontes palifer_ counted 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 Isopodous _Archæoniscus_ and 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 in _Journ. 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 of _Limulus_, several _Cytheres_ and allied genera, and a few Trilobites (_Phillipsia_ and _Griffithides_) belong to the strata of the Carboniferous System. In the Devonian System we find some minute entomostracans, the gigantic _Pterygotus_, 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, as _Phacops_, _Brontes_, _Cheirurus_, _Harpes_, and _Homalonotus_. The _Calymene Blumenbachii_ (_Lign. 175_, _figs._ 3 and 4) ranges through the Ludlow and Wenlock, to the Bala and Llandeilo formations. The _Phacops caudatus_ also (_Lign. 177_), the _Cheirurus bimucronatus_,[492] and the _Encrinurus punctatus_[493] extend from the Ludlow, to the Llandeilo formation. The Upper Silurian rocks exclusively contain some peculiar forms, as _Encrinurus variolaris_, _Bumastus Barriensis_, and several species of _Acidaspis_. And the Lower Silurian has several distinct genera, namely, the _Trinucleus_ (_Lign. 175, fig. 2_), _Ogygia_, _Agnostus_, _Asaphus_, _Olenus_, _Remopleurides_, &c. One species of _Pterygotus_, and one of _Eurypterus_, the _Ceratiocaris_ and _Hymenocaris_, and several species of the minute bivalved Entomostraca (_Leperditia_ and _Beyrichia_) are all that remain to be enumerated as constituting, in company with the _Trilobites_, 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 the _Limulus_ Group, and are named by him _Protichnites_. (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 the _Cyprides_ abound, thin slabs covered with these relics may be easily extracted; and many of the tertiary clays and sands yield _Cytheres_, together with _Foraminifera_ and 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 the _Enoploclytia Sussexiensis_ and _E. 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 figured _Foss. 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.

The _Cytheridæ_ of 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 figured _Lign. 172_, in which _fig. 2_ represents the nodule without any external indication of its contents, and _figs._ 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 such specimens 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: _Trilobites_ and _Beyrichia_.

Aberystwith, neighbourhood of. Silurian: _Trilobites_.

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

Atherfield, Isle of Wight. Wealden: _Cyprides_ in clay (_Lign. 174_).

Barr, Staffordshire; limeworks at Hay Head. Silurian: _Trilobites_,
particularly of the genus _Bumastus_.

Bewdley, Shropshire. Silurian: _Trilobites_.

Bolland, Yorkshire. Carboniferous Limestone: _Trilobites_ (_Cyclus_,
_Phillipsia_).

Burdie-house, near Edinburgh. Fresh-water coal-measures. _Cyprides_
and _Eurypteri_.

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

Coalbrook Dale. Coal-measures and Silurian. _Limuli_ and _Trilobites_.

Coniston, Lancashire. Silurian: _Trilobites_.

Dinley, Wilts. Purbeck. _Isopoda_ (_Lign. 171_) and _Cyprides_.

Dover. In the lower Chalk, _Astacus_ (_Enoploclytia_) _Sussexiensis_,
&c.

Dudley. Upper Silurian: _Trilobites_ in abundance.

Durlstone Bay, near Swanage. Purbeck: _Cyprides_ and _Isopoda_.

Folkstone, Kent. In Galt: small Crabs (_Lign. 168_), and numerous
_Cytheres_.

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: small _Crabs_, &c.

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

Scarborough. Oolite: _Astacidæ_, in clay nodules.

Sheppey. London Clay: _Lobsters_ and _Crabs_.

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

Tyrone, Ireland. Carboniferous and Silurian: _Trilobites_.

Wenlock, neighbourhood of. Upper Silurian: _Trilobites_.

Westbury, Gloucestershire. Lias: _Estheria_ and _Cyprides_.

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. the Arachnida (Scorpions and Spiders) and the Insecta, 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, termed _chitine_), 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 distinctions adopted 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 the _Coleoptera_ (sheathed-wings) comprise the beetles and other burrowing insects, in which the membranous wings are folded transversely beneath the elytra, or wing-cases. The _Orthoptera_ (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 termed _Homoptera_ (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. The _Heteroptera_ (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 the _Diptera_ (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 of _Trichoptera_ (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.

[495] Palæontologists are particularly indebted to the Rev. P. B. Brodie, F.G.S. for his compendious and valuable "History of the Fossil Insects in the Secondary Rocks of England" (8vo. 1845); and to J. O. Westwood, Esq. the eminent Entomologist, for the very important and interesting Observations on the Insect Remains, prefixed to the above work. In an interesting paper on the Geology of the vicinity of Ilminster, C. Moore, Esq. has noticed the numerous Insect remains of the Upper Lias of that place. Prof. E. Forbes and W. R. Binfield, Esq. have discovered Insects in the Hastings series; and Mr. Binfield, besides having most successfully searched the Upper Lias of Gloucestershire, has also detected some specimens in the Lias at Lyme. Lastly, Mr. Morris has found Insects in the Upper Lias in Lincolnshire.

ARACHNIDA.

Fossil Scorpion. (_Bd._ pl. xlvi′.)--The discover of a fossil Scorpion in coal-shale, associated with leaves, by Count Sternberg, and of Spiders in the limestone of Solenhofen, by Count Münster, proves the existence at a very remote period of both these insectivorous families of _Arachnidans_, or spiders (_Bd._ p. 405). The fossil Scorpion was found in a block of argillaceous shale, at Chomle, in Bohemia. It lies imbedded amidst the carbonized remains of leaves, and a large trifid carpolithe or seed-vessel (see _Bd._ pl. xlvi′.): by a fortunate separation of the shale, the back or dorsal carapace is shown on one surface; and the thorax, with five or six legs attached, and the abdominal segments, are exposed on the other, together with a fragment of the tail of another and larger Scorpion. The head and eyes, one of the jaws with teeth, and a portion of the skin remain (_Bd._ pl. xlvi. figs. 3, 4, 5, 6). The horny covering seems to have undergone no change; it is still elastic and transient, and consists of two layers, both retaining their texture, and structure, and exhibiting under the microscope hexagonal cells divided by strong partitions.

Fossil Spiders.--With the numerous insects preserved in the gypseous marls at Aix, of which we shall treat hereafter, Spiders are occasionally found. A beautiful example, showing the under surface of a small spider, with the papillæ of the spinning organs protruded by pressure, from the cabinet of Mrs. Murchison, is figured, _Bd._ pl. xlvi′. fig 12 In the beautiful lithographic stone of Solenhofen the remains of spiders are not unfrequent.

INSECTA.

Fossil Neuroptera.--Of this order, the insects of which are distinguished by their four finely reticulated membranous wings, several fossil species have been found. Some of these are referable to the family Libellulidæ;--insects so well known from their light and elegant figure, their beautiful and variegated colours, their large lustrous wings, and the velocity and gracefulness of their motions.

(_Drawn by Mr. Joseph Dinkel._)

In the cabinet of the late Marquess of Northampton.]

Fossil Libellulidæ. _Lign. 179._--Of the highly organized family of carnivorous insects, the _Libellulidæ_, five or six specimens have been discovered in the lithographic limestone of Solenhofen; a beautiful specimen from that locality is represented, _Lign. 179_. In this example both pairs of wings remain, but one wing is pressed down beneath the abdomen: the nervures of the wings are admirably preserved.

A few examples of the remains of this family have been found in the British strata. One species of _Libellula_ and one of _Æshna_ have been found by the Rev. Mr. Brodie in the Purbeck beds of the Vale of Wardour. Two species of _Libellula_,[496] two of _Æshna_, and some other allied species have been obtained by Messrs. Strickland, Buckman, Binfield, and Brodie from the Lias. The wing of the _Æshna liassina_, discovered in the Lias, near Binton, in Warwickshire, by Mr. Strickland, is two inches and ten and a half lines in length, and eight and a half lines in its greatest breadth, being one-third larger than the wing of the largest British species. See _Wond._ _Lign._ 119, and p. 528.

[496] A very interesting specimen of fossil _Libellula_, discovered by the Rev. Mr Brodie in the Upper Lias near Cheltenham, is figured in the Quarterly Geol. Journal, for 1848, vol. v. pl. v.

Fossil Corydalis. _Lign. 181, fig. 2._--The wing of a remarkable fossil Neuropterous insect was discovered by me in a nodule of ironstone, from Coalbrook Dale, and mistaken for a leaf. The specimen consists of one wing, which, as M. Audoin first ascertained, closely resembles that of the living _Corydalis_ of Carolina; see _Lign. 181, fig. 2_. The membranous structure and the distribution of the nervures are distinctly preserved; on the portion figured the surface of the wing lies in relief on the stone; and on the corresponding part of the nodule, a sharp imprint remains,[497] I have named this fossil in honour of the eminent French savant, M. Alex. Brongniart.

[497] This specimen is now in the collection of the British Museum.

Wings of _Corydalis_ have also been found in the Purbeck beds of the Vale of Wardour, by the Rev. Mr. Brodie, who has also discovered remains of _Phryganeidæ_ and a _Termes_ in the same group of strata.

Panorpa ? Liassica. _Lign. 180._--In the Lias, on the banks of the Severn, at Wainlode Cliff, Gloucestershire, specimens of minute neuropterous wings have been discovered. I subjoin accurate figures of two specimens in the cabinet of the Geological Society; they are represented twice the natural size; they resemble the wings of a recent genus of Neuroptera, termed _Panorpa_; particularly _P. Germanica_. The transverse lines are not fractures, but nervures, and are faithfully copied from the originals.

To the above notice of British fossil neuropterous insects, I may add that the wing of a large species (_Hemerobioides giganteus_) has been discovered by Dr. Buckland in the Stonesfield slate.

(_Drawn by S. P. Woodward, Esq._)

_Lias._ _Wainlode Cliff._

Portions of the anterior wings of a species resembling Panorpa.]

(_Drawn by S. P. Woodward, Esq._)]

Fig. 1.--Elytron, or wing-case of Buprestis Bucklandi, _Great
Oolite_; _Stonesfield_.
2.--Wing of Corydalis Brongniarti. (G. A. M.) _Carboniferous_;
_Coalbrook Dale_.

Fossil Coleoptera.--The _elytra_ or wing-cases of coleopterous insects have long since been noticed in the oolitic slate at Stonesfield, near Oxford; a locality celebrated for the only mammalian relies hitherto discovered in the Secondly strata of England. The Stonesfield elytra are always found detached; in no instance, I believe, has any other part of an insect been observed, except a single leg of a _Curculio_ (_Bd._ pl. xlvi′. _fig._ 10). The specimen figured _Lign. 181, fig. 1_, displays the usual characters of the largest species. These fossils are of a reddish-brown colour, with a finely granulated surface; there appear to be four or five species, all of which belong to _Buprestis_, a family of beetles remarkable for their splendid metallic lustre. Remains of _Coleoptera_ occur in the Tertiary clays near Corfe, Dorset,[498] and in the Lias of Worcestershire and Gloucestershire; and in the Danby oolitic coal-pits, in the eastern moorlands of Yorkshire, the elytra of beetles have also been discovered, by Mr. R. C. Taylor (_Bd._ vol. ii. p. 78).

[498] See Notice by the Rev. Mr. Brodie, Quart. Geol. Journ. vol. ix. p. 51.

A most remarkable fossil of this kind is described by Dr. Buckland; a unique specimen of _Buprestis_, from Japan, about an inch long, _converted into chalcedony_, with the antennæ and portions of the legs finely preserved. The surface of this insect is covered with clusters of minute concentric rings of chalcedony; an appearance common in silicified shells. Associated with this fossil, were fragments of silicified wood, bored with tubular cavities, apparently by the larvæ of insects of this family; and within these cavities was a quantity of dust produced by the boring, also converted into chalcedony (_Bd._ vol. ii. p. 78).

Of the Curculio, a genus of coleoptera distinguished by their splendid elytra, of which the _Diamond Beetle_ is a familiar example, the remains of two species have been discovered in the nodular ironstone of Coalbrook Dale, by Mr. W. Anstice, and are figured and described by Dr. Buckland (_Bd._ vol. ii. p. 76; and pl. xlvi′. figs. 1, 2). In one of these specimens (_Curculioides Ansticii_), with the exception of the rostrum and anterior part of the head, all the essential characters of the insect are displayed; namely, the elytra, thorax, and six legs, the hindmost of which exhibits the enlarged femur, or thigh, a character peculiar to the _Curculionidæ_. The legs possess a tufted appearance, which that eminent entomologist, Mr. Curtis, conceives may have been caused by fungi, after the death of the animal, as often happens in tropical climates. In the other example (_C. Prestvichii_), the insect lies on its back, with the left side raised upwards, and exhibiting a portion of the external surface of the left elytron; there are remains of the antennæ, and indications of the proboscis and of the legs.

(_Magnified six diameters._)]

_a, b._ Membranous wings of the _Corydalis_ type.
_c._ Punctate-striate elytron of a Beetle.
_d._ Elytron of a Beetle, with a smooth surface.
_e._ Smooth elytron, the upper part impressed with
transverse lines.

The _Orthoptera_, _Homoptera_, and _Diptera_ are also represented in the Lias of Gloucestershire, and in the Purbeck strata of the Vale of Wardour, by numerous species, which have been enumerated, and mostly discovered, by the Rev. Mr. Brodie.[499] This observer has, indeed, been very successful in his researches in the latter locality, for in the deposits of limestone and marl which yielded the isopodous crustaceans, previously described (p. 521, _Lign. 171_), he has discovered the remains of several orders of insects, and states that, for abundance and variety of specimens, the beds may be said to resemble the Tertiary marls of Aix and Œningen. These remains were obtained from a quarry at Dinton, about twelve miles west of Salisbury. They consist chiefly of _Coleoptera_, with the remains of _Neuroptera_, _Trichoptera_, and _Homoptera_, and of several species of _Diptera_. In the cream-coloured laminated Purbeck marls that axe exposed in Durlstone Bay (about one mile from Swanage) insectiferous beds have been found by the Rev. O. Fisher and Prof. E. Forbes, which are the equivalents of those of the Vale of Wardour; and similar beds were met with in the cutting of the railway through the Ridgway Hill, between Dorchester and Weymouth.

[499] See Brodie’s Fossil Insects.

In a quarry on the road-side between the village of Stone and Hartwell, Bucks, the Portland Oolite is covered by the Purbeck marls; in these latter remains of Insects occur, together with scales and teeth of small Fishes, and abundance of _Cyprides_.

All the British localities of fossil insects have now been alluded to; but on the Continent, independently of the celebrated limestones of Solenhofen, to which reference has been made, p. 550, there are several tertiary deposits exceedingly rich in these interesting fossils.

[Sidenote: FOSSIL INSECTS.]

Fossil Insects of Aix, in Provence.--The town of Aix is situated in the lowest part of a deep valley, the immediate flanks of which are composed of a thick fresh-water formation, lying unconformably upon strata of Jura limestone. The fresh-water series consists of white and grey calcareous marls, calcareo-siliceous grits, and beds of gypsum; and the quarries formed in the latter rock have long been celebrated for the prodigious quantity of fish and plants which they contain. M. Marcel de Serres first made known the great abundance of insects in these gypseous marls, and has enumerated nearly seventy genera, chiefly of the Coleoptera, Diptera, and Hemiptera; they are mostly referable to European forms, and to existing genera. An interesting Memoir on these strata, by Sir R. Murchison and Sir C. Lyell,[500] first directed the attention of the English reader to these beautiful fossils. In _Wond._ p. 261, an epitome of this valuable communication is given, and five specimens of insects are here figured, which will convey some idea of their forms and perfect state of preservation.

[500] Edinburgh New Philosophical Journal for October, 1829.

Fig. 1.--Tettigonia spumaria.
2.--Mycetophila; the body distended by pressure.
3.--Lathrobium.
4.--Allied to Penthetria holosericea. The hinder legs are
broken off, and one of them reversed, so that the _tarsi_
nearly touch the thigh; the _palpi_ are long and perfect;
the antennæ are remarkably distinct.
5.--Liparus; resembling L. Punctatus.

Fossil Insects of Œningen.--In the immediate vicinity of Œningen, near Constance, on the banks of the Rhine, there is the basin of an ancient lake, filled up with marls and limestones, presenting a fine example of a lacustrine formation, and abounding in fossil Fishes, Reptiles, Plants, Shells, Crustaceans, and Insects.[501] These Insects are often in an admirable state of preservation, and occur in the different stages of larva, pupa, and imago. The pupa of a _Libellula_ shows the mask, insertion of the legs, and the spiracula. Some belong to genera, the species of which frequent marshy plants of the same kind as those which are found associated with the insects; and it seems probable that they fell into the lake from the plants which grew on its borders, and became enveloped in the fine mud or sediment. Numerous species of several genera of Ants also occur in these deposits of Œningen and at Radoboj in Croatia.[502]

[501] See the Memoir by Sir R. I. Murchison on the lacustrine formation at Œningen, near Constance, Geol. Trans, new series, vol. iii. p. 277.

[502] See Prof. O. Heer’s Memoir, translated in the Quart. Journ. Geol. Soc. vol. vi. pt. ii. p. 61; and his History of Insects, ibid. p. 68.

[Sidenote: FOSSIL CADDIS-WORM.]

Fossil Larvæ of Phryganea. _Ly._ p. 185.--The _Caddis-worm_, so well known to all the brethren of the angle, is the larva of the winged insect termed _Phryganea_, and is abundant at the bottom of fresh-water streams and lakes; the cases, like those of the marine _Sabella_ (p. 385, _fig._ 6), are always studded over with extraneous bodies, cemented together by a glutinous secretion to the silken integument, or case, which encloses the lava. Some species are coated with pieces of stick or straw, others with minute shells, as planorbis, bithinia, and the like; and when the larvæ have passed into the perfect state, their cases, or _indusiæ_, remain. Many of the Tertiary fresh-water limestones of Auvergne are almost wholly composed of the _indusiæ_ of Caddis-worms, cemented together by calcareo-siliceous matter into stone, which is employed for building, and is called indusial limestone (_Wond._ p. 273). These limestones are associated with marls abounding in fresh-water shells and cyprides; the whole assemblage presenting all the stratigraphical and zoological characters of a lacustrine formation. "If," says Mr. Scrope,[503] "we consider that repeated strata, of five or six feet in thickness, almost entirely composed of these tubes, once extended over a district presenting a surface of many hundred square miles, we may have some idea of the countless myriads of minute beings which lived and died within the bosom of that ancient lake."

[503] On the Geology of Central France, by G. Poulett Scrope, Esq. 4 to. 1827.

On Collecting Fossil Insects.--The localities in which the British collector may reasonably expect to discover fossil remains of Insects, are Stonesfield, where the elytra of beetles are by no means scarce,--Coalbrook Dale, in which relics of this class are sometimes, but very rarely, found in the ironstone nodules,--Bedford, Warwickshire, and the Wainlode and Aust Cliffs, for Lower Lias insects,--Dumbleton and Ilminster, for Upper Lias insects,--Dallards, near Dinton, and Stone, near Aylesbury, and the exposures of similar beds in Dorsetshire, for the Purbeck insects.

The white clays belonging to the Bagshot series of Bournemouth, Poole, and Corfe, so rich in beautifully preserved leaves and other parts of plants, should be carefully searched for insect remains, since these clays at Creech, near Corfe, have already afforded a few specimens.[504]

[504] Quart. Geol. Journ. vol. ix. p. 51.

At page 549 a few other English localities yielding these delicate and very interesting fossils are also indicated as having been lately discovered by some of our most acute and active geologists.

Should the student visit the celebrated sites of these fossils in France and Germany, namely, Aix, Œningen, Solenhofen, &c., he will have but little difficulty in obtaining an interesting series, at a moderate expense.

The marls and limestones in which insects occur are often of a laminated character, and in general readily split asunder in the direction favourable for the display of the insects. In some examples, only the form of the animal is seen through a thin opaque pellicle of calcareous earth, which may be removed by a penknife or graver, and the wings, elytra, antennæ, legs, &c. will thus be disclosed. A very thin coating of mastic varnish heightens the colours of such specimens, and renders them more durable.