formation. Among these, two genera of bivalve shells, the species of which were formerly referred

(Encrinus monileformis.)

to anomia and terebratula, first appear, namely, producta and spirifera; in the older strata, which

we shall hereafter examine, various species of these shells will be found to swarm in the rocks.

25. THE SPIRIFERÆ.—I will in this place offer a few remarks on the spiriferæ, that I may introduce the interesting account of the structure of the recent analogues, by my friend Professor Owen, of the Royal College of Surgeons. The small subglobular bivalves, (terebratula,) 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 the organs of respiration. In the spiriferæ (Tab. 91, figs. 2, 6, 9, 10, 11,) there are two spiral appendages (hence the name of the genus) which are closely coiled, and are often, like the substance of the shell itself, changed into calcareous spar, (see figs. 2, 9); in specimens where the shell is removed, these organs may be seen in their original situation. The following description, by Mr. Owen, of a recent animal of the same family, a native of the South Seas, will explain the nature of this structure.

"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 of the arms. In Terebratula psittacea, a recent species (Tab. 91, fig. 6), two spiral arms, fringed at their outer margins, are seen to arise from these processes; these arms are quite

SERIES, &c.

Fig. 1. Producta punctata. 2. Spirifera trigonalis, with spiral processes, from the mountain limestone. 3. Producta depressa. 4. Bellerophon cornu-arietis. 5. Euomphalus pentangulatus; carboniferous limestone. 6. Recent terebratula psittacea, showing the spiral arms. ab, Cilia of the arms magnified. 7. Pentremites ellipticus; carboniferous formation. 8. Terebratula affinis. 9. Spirifera trigonalis. 10. Spirifera triangularis. 11. Spirifera octoplicata. 12. Orthoceratite. 13. Septum of orthoceratite.

free, except at their origins; when unfolded they are twice as long as the shell, and in a state of contraction are disposed in six or seven spiral gyrations, which decrease toward their extremities. The me

chanism by which the arms is extended is most beautiful and simple; the stems are hollow from one end to the other, and are filled with fluid, which being acted upon by the spirally disposed muscles composing the walls of the canal, is forcibly injected towards the extremity of the arms, which are thus unfolded and protruded. The respiration, as well as the nutrition, of animals living beneath a pressure of from sixty to ninety fathoms of seawater, are subjects of peculiar interest, and prepare the mind to contemplate, with less surprise, the wonderful complexity exhibited in the minutest parts of the frame of these diminutive creatures. In the stillness pervading these abysses, they can only maintain existence by exciting a perpétual current around them, in order to dissipate the water already loaded with their effete particles, and bring within the reach of their prehensile organs the animalculæ adapted for their support.

The spiral disposition of the arms is common to the whole of the brachiopodous genera, whose organization has hitherto been examined; and it is therefore probable, that in the fossil genus Spirifer, the entire brachia were similarly disposed, and that the internal, calcareous, spiral appendages were their supports.

If indeed the brachia of Ter.

psittacea had been so sustained, this species would have presented in a fossil state, an internal structure very similar to that of Spirifer."*

FISHES. Fifteen species, of a genus (Palæoniscus) supposed to be peculiar to this formation, have been discovered at Mansfeld; and ichthyolites of the same genus have been found in England, and in North America.

REPTILES.-Nine species are enumerated by authors of these some are referable to the crocodile, others to the ichthyosaurus and plesiosaurus, and a few belong to new or unknown genera; one is described by Dr. Jaeger, under the name of phytosaurus. Two genera have been found in the dolomitic conglomerate of this formation, near Bristol, by Dr. Riley and Mr. Stutchbury.

26. IMPRESSIONS OF THE FEET OF ANIMALS ON SANDSTONE. A few years since, the attention of geologists was called to the remarkable occurrence of the impressions of the feet of some unknown animal, on blocks of the new red sandstone, at Corncockle Muir, in Dumfriesshire; the prints were supposed to resemble those made by the paws of

* Tab. 91, fig. 6, page 475. Terebratula psittacea, with the perforated valve and lobe of the mantle removed to show the fringed brachia or labial arms, one of which has been artificially unfolded. (Zool. Trans. Pl. XXII. fig. 14.)

Fig. ab. A portion of the ciliary fringe of one of the spiral arms magnified.—Professor Owen on the Anatomy of the Brachiopoda, Zoological Transactions, vol. i. p. 145.