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Coal Measures and Coal Mining in Iowa, including paleontology and a discussion on the coal formation; also the methods of mining by Russell T. Hartman, 1898

Coal Measures and Coal Mining in Iowa by Russell T. Hartman, 1898, Page 137

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[page]136.[/page] [underlined][underlined][underlined][underlined]GASTROPODA.[/underlined][/underlined][/underlined][/underlined] The members of this class of the Mollusca have a more or less distinct head, and generally an unsymmetrical body. The mantle never has two lobes; the shell is univalve; the foot is well developed, and usually has the form of a disc upon which the animal creeps. The class is divided into two sub-classes. I. Branchiogastropoda. II. Pulmogastropoda. The Branchiogastropoda are constructed to breathe the air dissolved in water while the Pulmogastropoda breathe the air directly. In the former there may be true gills or the integument may act as an aerating organ.
 
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