CONTRIBUTIONS TO PALiGONTOLOGY. 147 



its course and margin marked by the prominence or greater width 

 of one of the interambulacral spaces on that side, owing to the 

 intercalation of the anal plate. 

 Surface striato-cancellate or striato-granulose. 



The structure given above differs in some essential features from that 

 usually recognized in these fossils. The narrow lanceolate space in the 

 centre of the interradial plates, which is always dififerently marked from 

 the portion on either side, and usually more elevated (though in one 

 species it is depressed), has been regarded as a distinct plate; but after 

 an examination of all the specimens accessible to me, I am unable to find 

 evidence of a suture-line bounding it; while on the anal side, the narrow 

 plate, which is nearly of the same form, is limited by a distinct suture- 

 line. I have therefore been compelled to give this signification to the 

 different parts. 



NUCLEOCRINUS ELEGANS. ^^ 



Nucleocrinus elegans : Conkad, Journal Acad. Nat. Sciences, Philadelphia, Vol. 



viii, p. 280. 1842. 



Nucleocrinus haHi, cited by Vanuxbm, Geological Report of the Third District 



of New-York, p. 163. 



General form subangularly ovoid or subelliptical, smaller at the 

 base, which is somewhat deeply concave at the point of attachment 

 of the column. The pseudambulacral fields are swollen out on the 

 sides and terminate in prominent angles below, giving the base a 

 pentangular form. The intervening or interradial spaces are 

 scarcely or but slightly concave above, but become distinctly so 

 below the middle and at the base. From the angles at the base of 

 the pseudambulacral areas, five well-defined ridges extend to the 

 margin of the column-cavity. Summit flattened. 



Easal plates small, extending only to the margin of the column- 

 cavity. Radial plates short, forming but a small part of the height 

 of the body, very slightly notched, and receiving only the base of 

 the pseudambulacral fields; their upper ends directed obliquely, 

 and fitting into the concave lower ends of the interradial plates. 

 On the anal side, the upper extremities on one side of two adjacent 

 radials are shorter than the others, owing to the extension of the 

 anal plate : interradial plate broad - lanceolate, except on the 

 anal side, where it is divided, leaving two narrow plates. Anal 

 plate sublanceolate, the base occupying the entire width between 

 the pseudambulacral fields. Poral pieces on each side the pseud- 

 ambulacral fields, from thirty-five to forty-three (in specimens of 

 different sizes). Centre of the summit occupied by five or more 

 small plates. 



