. Elements of geology : a text-book for colleges and for the general reader. Geology. SILURIAN ANIMALS. 307 (Tabulate) (Fig. 307, a), giving a cellular structure which may be finer or coarser. The Halysitids (Fig. 309) seem to be made up of small, hol- low, flattened columns with imperfect septa, united to form reticulating fluted plates, which on section have the appearance of chains crossing in all directions. These are also minutely tabulated. The Syringopo- roids (Fig. 308) are similar to the Halysitids, except that the hollow columns are cylindrical and connect with each other only in pla
. Elements of geology : a text-book for colleges and for the general reader. Geology. SILURIAN ANIMALS. 307 (Tabulate) (Fig. 307, a), giving a cellular structure which may be finer or coarser. The Halysitids (Fig. 309) seem to be made up of small, hol- low, flattened columns with imperfect septa, united to form reticulating fluted plates, which on section have the appearance of chains crossing in all directions. These are also minutely tabulated. The Syringopo- roids (Fig. 308) are similar to the Halysitids, except that the hollow columns are cylindrical and connect with each other only in places. Some of the more characteristic species of these families are given above (Figs. 305-309). There are many other forms than those mentioned above, but their affinities are little understood, and many are not true corals, but Polyzoa and sponges. Nearly all the corals of Silurian, in fact, of Palaeozoic times, fall under two orders—Rugosa and Tabulata. The Cyatho- phylloids are Eugosa, the other families mentioned are Tabulata. The Kugosa are character- istic of the Palaeozoic; the Tabulata are also nearly extinct: they have only one family living, viz., the milli- pores.* The Eugosa differ from modern star-corals in having their radiating septa in multiples of four, while modern star- corals have theirs in multiples of five or six. Hence star-cor- als have been divided into two types—a Palaeozoic and a Neo- zoic— the one four- parted (quadriparti- ta), the other six- parted (sexpartita). Halysitids are charac- teristic of Silurian; Favositids, of Siluri- an and Devonian; Fig. mi. Fig. 312. and CvatllOnhvlloids FlGS- 310-312.—Living Hydkozoa: 310. Sertularia phmata: a, nat- „ , " J. ural size; b. enlarged. 311. a and b, Different. Forms of Sertula- Of the PalCROZOic. ria. 312. Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these il
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
