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ART. VI. — Descriptions of fifteen new species of C^i^owt'^^ from the suh-carboniferous 

 limestone of Iowa, collected during the U. S. Geological Survey of Iowa, Wisconsin, 

 and Minnesota, in the years 1848-9. By David D. Owen, M. D., and 

 B. F. Shumard, M. D. 



Genus PLATYCRINUS, Miller. 

 Platycrinus planus. (New sp.) 



PI. 7, fig. 4, a, h, c. 



Basal plate. — Somewhat cup-shaped, consisting of a single piece, pentagonal, 

 smooth. The point for the attachment of the column is circular, slightly excavated, 

 and has a minute central perforation, for communicating with the canal in the 

 column. The surface of the plate is divided irregularly by three slightly raised 

 lines, which commence at the central perforation and extend to the superior margin, 

 with a corresponding obscure canal in the interior. The upper edges between the 

 angles of the pentagon are slightly concave, to accommodate the lower orbicular 

 edges of the superior plates. 



Superior 'plates. — Five, elongated, smooth, qnadrilateral. Their length is about one 

 third o^reater than their breadth. The excavations for the insertion of the arms are 

 rather deep, and occupy about one-half the breadth of the plates. 



Column. — Round, moderately large and striated in radii. 



Abdominal plates and arms unknown. 



In the appearance of its superior or arm-bearing plates, this species closely 

 resembles Flatycrinus elongatus of Gilbertson, (Phillips' Geology of Yorkshire, PL III. 

 figs. 24 and 26,) but may readily be distinguished from the latter by the form of its 

 pelvis, which is nearly cup-shaped, while that of Platycrinus elongatus is conical. 



Formation and Localities. — Occurs at Burlington, Iowa, in the sub-carboniferous 

 limestone immediately above the oolitic member of this formation, where it is 

 associated with Sjnrifer striatus, Productus punctatus, Orthis Michellini, Platycrinus 

 gramdatus, and various crinoidal remains. Its geographical range is quite extended 

 since it is also found at Button-mould Knob, seven miles south of Louisville, 

 Kentucky, in the blue shaly layers, interstratified with the fine grained micaceous 

 sandstone. 



The Platycrinus planus sometimes attains a large size, indeed larger than any 



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