The Medals of Creation, Volumes 1 and 2 / First Lessons in Geology and the Study of Organic Remains

by Gideon Algernon Mantell

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.