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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 112

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[page]111.[/page] Spirifer roissyi, d'Orbigny, 1847, Paleontology del'Amer. Merid., p.46. Terebatula subtilita, Hall, 1852, Stansbury's Grt. Salt Lake Rept., p.409. Spirigera subtilita, Meek and Hayden, 1859, Monogr. Brit. Carb. Brach., p.18. Athyris subtilita, Newberry, 1861, Ives Colorado Rept., p.126. Shells about medium size, ovoid, usually widest anterior to middle; as a general case, slightly longer than wide; double convex, becoming gibbous with age, hinge line very short. Dorsal valve with greatest convexity at or behind the middle; beak incurved under that of the other valve; in the antero-lateral portions are two depressions which divide the valve into three lobes, one being medial the others lateral. Ventral valve generally more convex than
 
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