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Charles Peach was the first to find, in 1854, three or four species of Orthoceras, also the genera Cyrtoceras and Lituites, two species of Murchisonia, a Pleurotomaria, a species of Maclurea, one of Euomphalus, and an Orthis. Several of the species are believed by Mr. Salter to be identical with Lower Silurian fossils of Canada and the United States.
Among the characteristic forms are Alveolites suborbicularis, also common to this formation in the Rhine, and Orthis arcuata, very widely spread in the North Devon localities. But we may expect a large addition to the number of fossils whenever these strata shall have been carefully searched.
a. b. a. b. a. b. Soft slates with subordinate sandstones fossils numerous at various horizons Orthis, Corals, Encrinites, etc. It will be seen that in all main points it agrees with the table drawn up in 1864 for the sixth edition of my "Elements." Mr.
I should like to present you with a memoir or monograph of mine, just published, on Spirifer and Orthis, but I will take good care to let no one pay postage on a work which, by its nature, can have but a very limited interest. . .I will await your arrival to give you these descriptions. I am expecting the numbers of your Fossil Fishes, which have not yet come. Humboldt often speaks of them to me.
Besides these, however, the same ancient schists have yielded two genera of brachiopods, Orthis and Orbicula, a Pteropod of the genus Theca, and four echinoderms of the cystidean family.
The prevailing fossils, besides corals and trilobites, and some crinoids, are several small species of Orthis, Cardiola, and numerous thin-shelled species of Orthoceratites. About six species of Graptolite, a peculiar group of sertularian fossils before alluded to as being confined to Silurian rocks, occur in this shale.
The next subdivision of the Upper Ludlow consists of grey calcareous sandstone, or very commonly a micaceous stone, decomposing into soft mud, and contains, besides the shells mentioned above, Lingula cornea, Orthis orbicularis, a round variety of O. elegantula, Modiolopsis platyphylla, Grammysia cingulata, all characteristic of the Upper Ludlow.
The Lower Silurian has been divided into, first, the Bala Group; secondly, the Llandeilo flags; and, thirdly, the Arenig or Lower Llandeilo formation. Orthis tricenaria, Conrad. Orthis vespertilio, Sowerby. Shropshire, N. and S. Wales. Two-thirds natural size.
As usual in bone-beds, the teeth and bones are, for the most part, fragmentary and rolled. Orthis elegantula, Dalm. Var. Orbicularis, Sowerby. Rhynchonella navicula, Sowerby.
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