. Elements of geology : a text-book for colleges and for the general reader. Geology. SILURIAN ANIMALS. Fig. 335. Fig. 336. Fig. 337. Figs. 333-337.—Silurian Crinoids and Asteroids: 333. Mariacrinus nobilissimus (after Hall). 334. Homocrinus scoparius (after Hall). 335. Heterocrine simplex (after Meek). 336. Protas- ter Sedgwickii. 337. Palaeaster Shsefferi (after Hall). Mollusks—Acephals or Bivalves.—Bivalves may be divided into two great sub-classes, viz., Lamellihranchs (leaf-gills) and Brachiopods (arm- feet). The valves of Lamellibranchs are right and left; those of Brachiopods are upper
. Elements of geology : a text-book for colleges and for the general reader. Geology. SILURIAN ANIMALS. Fig. 335. Fig. 336. Fig. 337. Figs. 333-337.—Silurian Crinoids and Asteroids: 333. Mariacrinus nobilissimus (after Hall). 334. Homocrinus scoparius (after Hall). 335. Heterocrine simplex (after Meek). 336. Protas- ter Sedgwickii. 337. Palaeaster Shsefferi (after Hall). Mollusks—Acephals or Bivalves.—Bivalves may be divided into two great sub-classes, viz., Lamellihranchs (leaf-gills) and Brachiopods (arm- feet). The valves of Lamellibranchs are right and left; those of Brachiopods are upper and lower, or dorsal and ventral. Brachiopods are much less highly organized than the other sub-class, and differ so essentially in their organization that some of the best naturalists re- move them not only from the class of Acephals, but from the depart- ment of Mollusca, and ally them rather with the Worms. Their gen- eral resemblance in external form to bivalves makes it more convenient to treat them under that head, until the question of their affinity is more definitely settled. Brachiopods are very abundant in the 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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