NEW SPECIES AND GENERA OF ORINOIDEA. 587 



SELENOIDES IOWENSIS. (N. S.) 

 (Tab. II. B, fig. 13.) 



Specific character. — One side flatly dome-shaped, the other ring-shaped, enclosing an umbilicus or 

 central depression. Small rhomboidal cells opening on the surface in curved rows, intersecting in arches; 

 the cells gradually increasing in size from the inner margin to the periphery. 



ARTICLE II. 



DESCRIPTIONS OF ONE NEW GENUS AND TWENTY-TWO NEW SPECIES OF CRINOIDEA, FROM THE 

 SUBCARBONIFEROUS LIMESTONE OF IOWA. BY D. D. OWEN, M.D., AND B. F. SHUMARD, M.D.* 



PLATYCRINUS. Miller. 



PLATYCRINUS PLANUS. (N. S.) 

 (Tab. V. a, fig. 4,a, b, 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, quadrilateral. Their length is about one-third greater 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 Platijcrimis elon- 

 gatus of Gilbertson (Phillips's Geology of Yorkshire, PI. III., figs. 24 and 26), but may readily be distin- 

 guished from the latter by the form of its pelvis, which is nearly cup-shaped, while that of PlaUjcrinus 

 elongatus is conical. 



Formation and localities. — Occurs at Burlington, Iowa, in the subcarboniferous limestone immediately 

 above the oolitic member of this formation, where it is associated with Spirifer striatus, Productus punc- 

 tatus, Orthis MichelUni, Platycrinus granulatus, 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 of the genus with which 

 we are acquainted : a specimen from Burlington, though devoid of the abdominal plates, is nearly two 

 inches in diameter. 



PLATYCRINUS YANDELLII. (N. S.) 

 (Tab. V. a, fig. G, a, b.) 



Basal plate. — Somewhat massive, pentagonal, flattened, and rather deeply excavated at the point where 

 the supra-columnar joint is attached ; with a minute perforation in the centre corresponding to the canal 



* Collected during the United States Geological Survey of Iowa, Wisconsin, and Minnesota, in the years 1848-49. 

 Originally published in the Jour. Acad. Nat. Sci. Phila., New Series, Vol. II., Parts 1 and 2 ; now modified by ad- 

 ditions anil researches since that article appeared. 



