Beautiful ammonite from the USA, South Dakota, with original pearly shell.

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Original reference :

Morton, S. G. 1842. Description of some new species of organic remains from the United States Cretaceous Group with a tabular view of the fossils so far discovered in this formation. Journal of the Academy of Natural Sciences of Philadelphia 8 (2): 207-227. [P. 209, pl. 10, fig. 3]. Neotype: YPM 27222 (Morton-type plaster cast is ANSP 51563). PaleoDB taxon number: 145232. Synonyms :? Ammonites mandanensis Morton, 1842 (source: Landman and Waage, 1993); ? Ammonites abyssinus Morton, 1842 (source: Landman and Waage, 1993). References: Landman and Waage (1993). Origin of the name: Named by Joseph Nicolas Nicollet, "who explored and mapped the upper valley of the Mississippi River and collected Cretaceous fossils in South Dakota in 1839" (Cobban et al., 2006, p.33). Original description: A. Nicolletii. PI. 10, fig. 3.-Convex shell, rapidly enlarging towards the mouth, with at least two volutes, one received deeply in the other; delicate coast, gently curved, and bifurcated towards the convex dorsal periphery, which they cross in arched lines, between numerous minute tubercles. I am very pleased to dedicate this interesting species to my friend Mr. Nicollet, whose zeal and intelligence have contributed in large part to the development of American science. A few years ago I saw several specimens of Ammonites that were obtained by Judge Bry, in the town of Wachita, Louisiana. I have elsewhere (Synop, 24), I consider them as indications of Cretaceous deposits; and my memory leads me to believe that their characters correspond either to A. abyssinus or A. Nicolktii.