seven spiral gyrations, which decrease towards their extremities. It has been conjectured, that, as the stems are hollow from one end to the other, and filled with fluid, this might be acted upon by the spirally, disposed muscles composing the walls of the canal, and forcibly injected towards the extremity of the arms, which would be thus unfolded and protruded. None, however, of the living specimens of this animal observed by Mr. Barrett,* in 1855, protruded their arms; but these organs were extended just so much that the cirrhi, when unbent, came as far as the margin of the shell.

The arrangement of the fringed arms in the known living Brachiopoda is generally either more or less perfectly spiral, sigmoid, looped, or folded. In the fossil genera Spirifer, Athyris, Merista, Retzia, Uncites, and Atrypa, the internal, calcareous, spiral appendages were evidently the supports of perfectly spiral arms. If indeed the arms of Rhynchonella were so supported, that genus would present the same structure as that of Atrypa, and a close analogy to that of the Spiriferida.

46. CRUSTACEANS AND INSECTS.-With the layers of fresh-water shells that are intercalated in some of the coaldeposits, there are a few species allied to water-fleas, Cypride. They occur abundantly in the Nova-Scotian and some of the Pennsylvanian coal-measures; also in the Shrewsbury, Ashby-de-la-Zouch, Border-country, and Burdie-House coalstrata. In the last, and near Glasgow, two species of a peculiar entomostracous crustacean, Eurypterus,† one of which is twelve inches long, have been discovered by Dr. Hibbert.

Dithyrocaris is another peculiar form of the lower tribe of crustaceans not uncommon in some of the carboniferous strata of Ireland and Scotland.

In the ironstone-nodules of Coalbrook Dale, the remains of small crustaceans sometimes form the nucleus, and Mr. Prestwich § discovered some in a good state of preservation (Lign. 182). Some of these crustaceans are referable to the Limu

Annals Nat. Hist. 2nd ser. vol. xvi.
Medals, p. 524.

Geol. Transact. 2nd ser. vol. v. p. 41.

p.

257.

Medals, p. 525.

The chemical changes which have taken place in the carboniferous strata, and led to the formation of the bands and nodules of ironstone, are thus explained by Sir H. de la Beche:-The argillaceous

lus, or King-crab; a genus which is abundant in the seas of India and America. The Limulus is one of the lower Crustacea (Entomostraca), and has a distinct carapace or buckler, and the last segment is prolonged into a point or style; it has two eyes in front of the shield, and the gills are disposed on lamelliform pro

cesses.

iron-stones are formed of carbonate of iron, mingled mechanically with earthy matter, commonly corresponding with that constituting the shales with which they are associated. Mr. Hunt, of the Museum of Economic Geology, instituted a series of experiments to illustrate the production of these clay-ironstones, and he found that decomposing vegetable matter prevented the further oxidation of the protosalts of iron, and converted the peroxide into protoxide of iron, by taking a portion of its oxygen to form carbonic acid. Under the conditions necessary for the production of the coal distributed among the sand, silt, and mud, the decomposition of the vegetable matter would necessarily form carbonic acid, among other products. This carbonic acid, mixed with water, would spread with it over areas of different dimensions according to circumstances; forming salts and meeting with the protoxide of iron in solution, it would unite with the protoxide, and form a carbonate of iron. The carbonate of iron in solution would mingle with any fine detritus which might be held in mechanical suspension in the same water; and hence, when the conditions for its deposit arose,-which would happen when the needful excess of carbonic acid was removed, -the carbonate of iron would be thrown down, intermingled with the mud; and, if not in sufficient quantity to form continuous layers, would aggregate into nodules, and be arranged in planes amid the sediment.-Memoirs of the Geological Survey of Great Britain, vol. i. p. 185. See also Prof. W. Rogers on the Carbonate of Iron in the Coal-Measures, Silliman's Journal, vol. xxi. p. 339; Mr. Binney on the Origin of Iron-stones, Mem. Lit. Phil. Soc. Manchester, vol. xii. p. 31; and a paper by Dr. Hooker and Mr. Binney on some limestone-nodules, in the bituminous coal of the Lancashire coal-field; Proceed. Roy. Soc. vol. xii. p. 188.

*Buckland, Bridg. Treat. p. 396.

It is in the carboniferous system that we first meet, in a descending order, with vestiges of the extinct family of crustaceans called Trilobites* (Griffithides, Phillipsia, &c.); but, as these animals are especially characteristic of the older rocks-the Silurian, I shall reserve a particular notice of them for the next discourse.

The higher Crustacea are still but little known in the coal-rocks. The Gampsonyx,† however, of the Saarbrück coal, combines some characters now found in the Amphipods and the Decapods; and the Pygocephalus ‡ of the Manchester coal-shales, another rare form, is referable either to the lower Decapods or to the Stomapods.

Insects.-The remains of insects belonging to several genera have been found in the carboniferous series of England and Europe. From the ironstone-nodules of Coalbrook Dale, several species of beetles, related to the Curculio or diamond-beetle, have been obtained. In a nodule from the same locality I discovered the wing of a large neuropterous insect, closely resembling a species of living Corydalis of Carolina.§ The coal-measures of South Wales have also yielded insect-remains.

Numerous specimens of orthopterous, neuropterous, and coleopterous insects have been described by F. Goldenberg¶ from the coal-basin of Saarbrück, in Rhenish Prussia, whence so many other interesting fossils have been obtained.

Fossil Scorpion.-Not only are the remains of insects imbedded in the coal-strata, but also those of animals to which they served as food. A fossil Scorpion has been discovered by Count Sternberg in carboniferous argilla

* Medals, p. 532.

† Jordan and von Meyer, Palæontographica, vol. iv. p. 1, pl. i. Huxley, Journ. Geol. Soc. vol. xiii. p. 363, pl. xiii.

§ Medals, p. 554.

This specimen is now in the British Museum.

|| In the collection of the Rev, S. Lucas, F.G.S.

¶ Palæontographica, vol. iv. p. 17, plates iii. to vi.

ceous schist, at Chomle, S.W. of Prague, in Bohemia.* This fossil is about two inches and a half long, and is imbedded in coal-shale, with leaves and fruits. The legs, claws, jaws, and teeth, skin, hairs, and even portions of the trachea, or breathing apparatus, are preserved. It has twelve eyes, and all the sockets remain; one of the small eyes and the left large eye retain their form, and have the cornea, or outer skin, preserved in a corrugated or shrivelled state. The horny covering is also preserved; it is neither carbonized nor decomposed, the peculiar substance of which it consists, elytrine, having resisted decomposition and mineralization.

47. FISHES OF THE CARBONIFEROUS SYSTEM.-The fishes of the coal† are of the placoid and ganoid groups (see p. 352): and several of the genera have not been found in any other system; all of these have the heterocercal form of tail (see p. 531). Sixty genera have been determined from the carboniferous strata of the British Isles. I can only allude to a few of the most characteristic.

Amblypterus.-This is a genus restricted to the coal-measures, and is charactererized, as its name implies, by very large and wide fins composed of numerous rays. The scales are rhomboidal and finely enamelled; and the teeth are small, numerous, and set close together like the hairs of a brush; indicating that these fishes fed on decayed seaweeds and soft animal substances. The tail is a good example of the heterocercal type. A restored outline of the fish is given in Lign. 183, from M. Agassiz's great work, the "Poissons Fossiles." Four species have been found in no

See Verhandl. Gesell. vat. Mus. Böhmen, 1835, p. 35; Dr. Buckland's Bridgewater Treatise, plate 46, p. 406, et seq.

See some interesting remarks on the fishes of the North American coal-beds, by Mr. Newberry, in the Edinb. New Phil. Journ. New series, vol. v. p. 364; and by Messrs. Worthen and Agassiz, ibid. p. 367.

dules of ironstone at Saarbrück, on the borders of Lorraine; and at Newhaven, near Leith.

*

Megalichthys. Of the remarkable group of fishes termed Sauroid, the remains of two genera have been discovered in the strata at Burdie House by Dr. Hibbert, and subse

LIGN. 183.-RESTORED FIGURE OF THE AMBLYPTERUS; A HETEROCERCAL FISH PECULIAR TO THE CARBONIFEROUS SYSTEM: one-sixth the nat, size,

a, The upper lobe of the tail, into which the vertebral column is prolonged.

quently in several other localities. The Megalichthys was covered with enamelled, quadrangular, finely granulated scales, very thick, and nearly an inch wide. The head was protected by strong enamelled plates. It had very large teeth, which were conical, hollow, and striated. This fish was

from three to four feet in length.

Holoptychius.-This is a genus of gigantic sauroid fishes, some species of which attained a length of thirty feet. The scales are thin and nearly circular, the upper surface corrugated in ridges, and from one to five inches in diameter. The plates covering the head have a shagreen-surface with irregular ridges. It has large conical sauroid teeth of great density; and numerous long slender teeth.

Cestracionts.t-Remains of numerous extinct species of

*Medals, p. 615.

Medals, p. 583.