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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 59

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[page]58[/page] are more than two rows of inter ambulacral plates, and more than two rows of ambulacral plates. The plates may be thick and rigid or they may be thin. [underlined]Archaeocidaris[/underlined], McCoy. Echinocrinus, Agassiz. Paleocidaris, Desor. Spherical or depressed spheroidal ambulacra comparatively narrow and composed of two ranges of small plates with two pores to each plate. Inter ambulacral plates large, thin, and each provided with a large perforated central tubercle, surrounded at its base by a smooth ring, and rounded for the articulation of the primary spine surrounding the whole is a more or less complete circle of marginal or sub-marginal smaller spines. Apical disc
 
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