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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 108

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[page]107.[/page] margin; area narrow, mesial fold well marked, angular on young individuals, rounded on adult specimens commencing at beak, widening, and becoming higher anteriorly. Ventral valve with very prominent incurved beak, hinge area wide broadly triangular, concave, extending to ears; foramen a sub-equilateral triangle; a deep trough like sinus which broadens and deepens as the front is approached. Surface marked by radiating plications which are in turn ornamented several [inserted]longitudinal[/inserted] striae; shell also marked by lines of growth. Geol. Pos. Coal Measures. Loc.-- Braddyville, Iowa; LaSalle, Illinois; etc. Reference. Final Rept. U. S. Geol. Survey of Nebraska, p.183.
 
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