periodical inundations from mountain-torrents, poured down from alpine regions on which the pines and other coniferæ, associated with the arborescent ferns of the coal, may have flourished? Would not such physical conditions, modified by occasional changes in the relative level of the land and water by subterranean movements, meet the exigences of the case? 44. ZOOPHYTES AND ECHINODERMS OF THE CARBONIFEROUS SYSTEM.-We must now briefly notice the animal remains entombed in the deposits that are associated with those which have proved so rich and varied a field of botanical research. The Zoophytes and Molluscs are for the most part marine, and in a great measure confined to the limestones below the coal. There are but doubtful evidences of the Sponges in these beds; but Foraminifera often abound. Textularia and Endothyra have been discovered by Prof. Phillips * in slices of limestone from Yorkshire and Westmoreland, and by Mr. Sorby in some mountain-limestone from Shropshire. Nodoraria has been found in the carboniferous rocks of Tyrone, by M'Coy; a Nummulite-like form occurs in the mountain-limestone both of Shropshire and of Russia; ‡ and one of the most characteristic fossils of the mountain-limestone of the Lower Volga in Russia, § and of the Ohio in North America, is the Fusulina; white limestones and calcareous shales being almost wholly composed of this little shell (F. cylindrica), which resembles a grain of wheat or rice, and is allied to the Nonionina. A second species has been detected in the carboniferous limestone of the Arctic Regions, by Mr. Salter.|| * Trans. Polytechn. Soc. Yorkshire, 1846, p. 277. † Annals Nat. Hist. vol. xiii. p. 131. Bullet. Imp. Soc. Nat. Moscow, 1849, vol. xxii. p. 337 "Belcher's "Arctic Voyage," vol. ii. Appendix. * The Corals amount to very many species, chiefly belonging to the genera Alveolites, Amplexus, Aulopora, Chatites, Clisiophyllum, Cyathophyllum, Lithodendron, Lithostrotion, Michelinia, Nematophyllum, Syringopora, and Zaphrentis. Of Bryozoa, Fenestella is the most common genus in this formation. The mountain-limestone swarms with Crinoidea; and entire beds are made up of their petrified remains, as was explained in the former Lecture (see p. 660). Elegant and abundant species of Actinocrinus, Cyathocrinus, Platycrinus, Poteriocrinus, and Rhodocrinus combine to characterize the carboniferous limestones and shales; but several of rarer occurrence are also found. A singular type of Crinoideans, named Pentremites† (Lign. 181, fig. 7), also abounds in the mountain-limestone, both in England and America ‡ (see p. 666). Other echinoderms of a peculiar character (Archæocidaris and Palachinus) are not unfrequent in the carboniferous limestone of Ireland and Yorkshire. 45. SHELLS OF THE CARBONIFEROUS SYSTEM. The remains of nearly 800 species of the various tribes of mollusca have been obtained from this formation in the British Isles alone. About twenty species of bivalve shells, having close alliances with existing genera of shells living in fresh or brackish waters, and therefore indicative of their own fresh-water or estuarine origin, occur in some of the coal-measures. These fossil genera comprise Anthracosia,§ Cardinia, Myalina, Mytilus, and Unio; and some of the species abound in some parts of the coal-measures in extensive, though thin, beds of shale or limestone, known as "mussel-bands." See Milne-Edwards and J. Haime's beautiful Monograph, published by the Palæontographical Society, 1852. + Comprised in the Blastoidean Order of the Echinodermata. Medals of Creation, vol. i. p. 297. § See Prof. King's interesting paper on the distinctive characters of this member of the Unionidæ, in the Annals Nat. Hist. 2nd ser. vol. xvii. p.51. The marine shells of the carboniferous rocks are in a great measure limited to the limestone and shales below the coal. Exceptional instances, however, have been already mentioned. Many species of gasteropodous spiral univalves abound in some of the limestones. Pleurotomaria and Euomphalus are the most frequent; the latter is remarkable from its inner volutions being traversed by imperforate septa.† Some limpet-like gasteropods are also found, such as Capulus and Patella. A very common and characteristic univalve is the Bellerophon ‡ (Lign. 181, fig. 4), usually referred to the Nucleobranchiate division of the Gasteropoda.§ The most interesting Gasteropod of the coal-series is a pupa-like shell, probably a land-snail, of which one or two specimens were found, together with the remains of a little batrachian reptile, by Sir C. Lyell and Mr. Dawson, in an upright fossil tree-stump in the coal-measures of NovaScotia. The cephalopodous shells found in the mountainlimestone of Britain and Ireland, and in the associated strata, amount to upwards of 130 species. The Ammonite of the secondary formations is in this system abundantly represented by its near ally, the Goniatites; ¶ and the Nautilus ** and the Orthoceras †† almost rival the Goniatite in numbers. The Orthoceras (Lign. 181, fig. 12) may be described as a straight Nautilus, of an elongated and cylindrical shape, tapering to the extremity, and having entire septa, pierced by a siphuncule (fig. 13). The Orthoceratites are often from twenty to thirty inches in circumference at the largest extremity, and upwards of seven feet in length. Numerous bivalves of genera closely related to, if not identical with, the existing Avicula and Pecten also occur; and other bivalves, such as Cypricardia, Conocardium, Ed Medals, p. 428. *See above, p. 676. Quart. Journ. Geol. Soc. vol. ix. p. 58, pl. iv. Medals, p. 465. Medals, p. 482. ** Medals, p. 467. ++ Medals, p. 475. mondia, Leda, Modiola, Nucula, Sanguinolites, and Sedgwickia. But the most striking modification in the molluscous fauna is the abundance of extinct types of Brachiopoda * or Palliobranchiata,† such as Athyris, Chonetes, Leptana, Lingula, Orthis, Productus, Rhynchonella, Spirifer, Strophomena, &c. These occur in profusion; and entire beds of limestone sometimes are aggregations of the shells of these curious animals. As we descend to the more ancient rocks, we shall find these fossils yet more prevalent; and I will, therefore, in this place offer a few remarks on the structure of this family of mollusca. The small subglobular bivalves, Terebratulæ, § so abundant in the chalk, are sometimes found empty, and, if the valves be carefully separated, two curious appendages are seen projecting from the hinge into the interior of the shell; these processes are the internal skeleton for the support of ciliated organs for the production of currents in the water. In the Spirifers (Lign. 181, figs. 2, 9, 11), there are two spiral appendages || which are closely coiled, and are often, like the substance of the shell itself, changed into calcareous spar (figs. 2, 9); in specimens where the shell is removed, these organs may be seen in their original situation. The loop-like processes observable in the interior of the shells of many of the fossil Terebratulæ are the internal skeleton, and are for the attachment of the muscular stems, or stalks of the fringed arms, or lateral prolongations of the lips of the animal. These arms, or oral appendages, are fringed with cirrhi, probably covered with microscopic cilia; and by the vibratile action of the latter minute particles of food are transmitted Arm-foot: the spiral arms of some of these molluscs were at first supposed to serve to some extent as locomotive organs; hence this mostused name. Mantle-gilled: the animals having no special branchiæ or gills, their blood is aërated through the medium of their inner integument or mantle hence this philosophically correct, but neglected name. See Owen "On the Anatomy of the Brachiopoda," Zoological Transactions, vol. i. p. 145; "Lectures on Comp. Anat." &c.; Woodward's "Manual of Mollusca," p. 209; and Davidson's "Monographs of the British Fossil Brachiopoda," published by the Palæontographical Society (especially the Introduction) § Medals, p. 388. Hence the name of the genus (coil-bearing). towards the mouth. In Rhynchonella psittacea, a recent species (Lign. 181, fig. 6), two spiral arms, fringed at their outer margins, are seen to arise from processes having the form of lamellar plates; these oral arms are quite LIGN. 181.-SHELLS AND CRINOIDS, CHIEFLY FROM THE PALEOZOIC STRATA. Mountain-limestone. Fig. 1. Productus punctatus. 2. Spirifer trigonalis. 4. Cast of Bellerophon cornu-arietis. 5. Euomphalus pentangulatus. 7. Pentremites ellipticus. 9. Spírifer trigonalis, showing one of the spiral processes in situ. 10. Spirifer triangularis. 12. Orthoceras laterale. 13. Septum of the same. Wenlock limestone. Fig, 3. Leptæna depressa. 8. Atrypa reticularis. 11. Spirifer elevatus. Recent. Fig. 6. Rhynchonella psittacea, showing the fringed spiral brachia or arms, and one of them artificially extended; the perforated valve and the lobe of the mantle are removed. Fig. a b, a portion of the fringe of cirrhi, magnified. free, except at their origins; when unfolded, they are twice as long as the shell, and in their natural state of contraction are disposed in six or |