PALEONTOLOGY. 447 



.SPECIES FROM THE LIMESTONES ABOVE THE "BONE- 

 BED," IN THE VICINITY OF COLUMBUS, OHIO, AND 

 NOT KNOWN TO OCCUR BELOW THAT 

 HORIZON. 



ECHINODERMATA. 



CRINOIDEA. 



Genus GILBERTSOCRINUS Phillips. 



Gilbertsocri7ius spinigems. 



Plate VII, fig. 12. 



Trematocrinus spinigerus Hall, 15th Rept. State Cab., p. 128. 



Gitbertsocrmus (Trematocrinus) spinigerus Hall, Descript. of New Species of 

 Grinoidea from the Carboniferous rocks of the Mississippi valley, Plate I, fig 9. 



Body small, of nearly equal height and width, broadly truncated at the base, 

 slightly rounded and expanded in the lower half of the height, but generally con- 

 tracted above to the base of the arms. The base of the cup. is deeply impressed, 

 including the basal and sub-radial plates; the first radials form the lowest part of 

 the cup, the second radials are placed at the point of its greatest diameter, and the 

 third at about one-half the entire height. The first and second radials are compar- 

 atively large, the first being heptagonal, the second hexagonal, and the third which 

 are smaller than the second are heptagonal, obtusely cuneiform above, and support 

 on each sloping face two proportionately large supra-radial plates, one above the 

 other, the upper face of the second one of which is excavated and its surface cica- 

 trized for the attachment of the true arms, while the summit arms arise from above 

 and are formed by the junction of the plates from the two adjacent rays. The first 

 interradial plates are moderately large, are truncated below the rest on the upper 

 truncated ends of the subradials, thereby separating the first radials of the adja- 

 cent rays from each oth^r. Above the first interradials the plates are in arches of 

 ^•hree plates each for two or three transverse ranges with two and then one at the 

 top, except in a single lateral area where there is but two plates transversely. 



The anal area is somewhat larger than the other areas, but the arrangement of 

 plates cannot be determined from excess of silicification. The inter-supraradial 

 areas are marked by two plates in each, situated one above the other, the second 

 one having its upper end forming a part of the summit or dome of the crinoid. 

 The summit arms have been small but proportionately strong at the base, the ear- 

 lier series of plates only being reserved. 



The surface of the plates has been elevated in the middle and perhaps ridged in 

 a stellate manner, but they are too small and too much weathered to allow of a per- 

 fect determination of this feature. The centre of the radial series is elevated so as 

 lo form a distinctly marked ridge traversing the series from and above the third 

 radial ; while the first and second radials bear short obtusely rounded spines, of a 

 length somewhat greater than the diameter of the plate. The spines of the first 

 radials project outward and downward at an angle of nearly iorty-five degrees to the 

 line of the base, while those of the second radials are a little inclined below a hori- 

 zontal. 



