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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 96

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[page]95[/page] Dorsal valve concave, no mesial sinus or fold. Ventral valve convex, greatest convexity in umbonal region, descending abruptly to ears, beak incurved, over hinge line, spine bases rather numerous. Surface marked by rather coarse irregular, radiating costae and on the ears by wrinkles. Geol. Pos.-- Des Moines stage Coal Measures. Locality Des Moines, Iowa. [underlined][underlined]Orthidae[/underlined][/underlined] The articulation in this family is by means of teeth and sockets and a hinge line. The hinge line is straight and is usually shorter than the greatest width of the shell. Both valves have hinge areas with an open delthyrium in adult stages. Surface [underlined]usually[/underlined] ribbed.
 
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