. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 637.—Cycas circinalis, x ^v, a Living Cycad of the Moluccas (after Jjecaisne). Fig. 638.—Stem of Cycadeoidea megalo- phylla, x J. Echinoderms, the Crinids, or plumose-armed Crinoids, are very abun- dant and very beautiful; in fact, they seem to have reached their high- est point in abundance, diversity, and gracefulness of form (Figs. 640, 641). But the free forms, Echinoids and Asteroids, are now equally abundant (Figs. 642-644). Brachiopods are still abundant, though far less so than formerly; but they
. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 637.—Cycas circinalis, x ^v, a Living Cycad of the Moluccas (after Jjecaisne). Fig. 638.—Stem of Cycadeoidea megalo- phylla, x J. Echinoderms, the Crinids, or plumose-armed Crinoids, are very abun- dant and very beautiful; in fact, they seem to have reached their high- est point in abundance, diversity, and gracefulness of form (Figs. 640, 641). But the free forms, Echinoids and Asteroids, are now equally abundant (Figs. 642-644). Brachiopods are still abundant, though far less so than formerly; but they now belong almost wholly to the modern or sloping-shouldered types, such as Terebratula and Rhynchonella. Only a very few small specimens of the Paleozoic type linger until the Lias. Lamellibranchs, or common bivalves, are extremely abundant. Among the common and characteristic forms are Trigonia, Gryphaea, and Exogyra, belonging to the oyster family; and the strangely-shaped Diceras (Fig. 645). It is interesting, also, to observe here the first appearance of the genus Ostrea (oyster). Cephalopods.—One of the most striking characteristics of the Juras- sic period is the culmination of the class of Cephalopods in number, diversity of forms, and, if we except some of the Silurian Orthocera- tites, in size. They were represented by the Ammonites and the Be- lemnites, the one belonging to the order of Tetrabranchs, or shelled, the other to the Dibranchs, or naked Cephalopods. It is important to. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original LeConte, Joseph, 1823-1901. New York : D. Appleton and Co.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
