. Elements of geology : a text-book for colleges and for the general reader. Geology. 318 PALEOZOIC SYSTEM OF ROCKS. shells, with simple sutures and a central or subcentral siphon-tube (siphuncle). The siphuncle of the family was large in proportion to a b. Fig. 361 Fig. 361.—Showing Structure of Orthoceratite. a, Ormoceras ; b, Actinoceras ; c, Huronia : d, Sec- tion of Siphuncle of Huronia. Fig. 3G2.— Kestoration of Orthoceras, the shell being supposed to be divided vertically, and only its upper part being shown: a, arms; /, muscular tube (" funnel ") by which water is expelled fr
. Elements of geology : a text-book for colleges and for the general reader. Geology. 318 PALEOZOIC SYSTEM OF ROCKS. shells, with simple sutures and a central or subcentral siphon-tube (siphuncle). The siphuncle of the family was large in proportion to a b. Fig. 361 Fig. 361.—Showing Structure of Orthoceratite. a, Ormoceras ; b, Actinoceras ; c, Huronia : d, Sec- tion of Siphuncle of Huronia. Fig. 3G2.— Kestoration of Orthoceras, the shell being supposed to be divided vertically, and only its upper part being shown: a, arms; /, muscular tube (" funnel ") by which water is expelled from the mantle-chamber; c, air-chambers; s, siphuncle (after Nicholson). the shell, and had often a beaded structure (Fig. 361, «, #, c, d). The genera are founded largely on the form of this part. They existed in great numbers, and attained very great size. Speci- mens have been found fifteen feet long, and eight to ten inches in diam- eter. They were, without doubt, the most powerful animals of that time, the tyrants and scavengers of these early seas. We give, in Fig. 357, a restoration of the creature. They are entirely characteristic of the Palaeozoic ; commencing in the Primordial, extending through into the Carboniferous, and passing out there. They attained their maxi- mum of devolopment in size and number in the Silurian. Although straight-chambered shells (Orthoceratites) are most abun- dant and characteristic, and also the earliest, coiled shells of the same tribe (Nautiloids) are also found, and some of them of considerable size, but not until the upper Silurian. Some of these are close-coiled shells, true Nautilus family; others open-coiled, and more nearly allied. 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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