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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 153

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[page]152[/page] about five in number, gradually increasing in size from center outward; obliquely flattened on periphery which is bordered both above and below by narrowly rounded ridges. Aperture irregularly quadrilateral. Surface marked by strong irregular striae which give to the peripheral carinae a nodular appearance. Geol. Pos.-- General in Coal Measures. Ref.-- Geol. of Missouri, Vol. V., p.160. [underlined][underlined]Neritopsidae[/underlined][/underlined] In this family the shell is thick, globular, without an umbilicus. The aperture is entire, oval, or semilunate. It posesses [possesses?] a thick shelly operculum, which is oval in shape and not spiral.
 
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