PAL^ONTOLOQICAL REPORT OF GEOLOGICAL SURVEY. 483 



high as wide; lying deep in the columnar-pit, and frequently conceal- 

 ed by the insertion of the columns, as in fig. 2c, plate IV. 



First radial pieces five ; hexagonal ; nearly equal in size ; twice as 

 broad as high; ornamented by sculptured ridges, which terminate at 

 a longish or rounded knob, near the margin of the columnar depres- 

 sion. 



Second radial pieces five; sub-quadrangular; wider than high ; near- 

 ly of the same size; the center of the pieces are ornamented by a 

 knob, which terminates at this upper margin. In specimens of the 

 aged of this species the knob is frequently prolonged, and assumes the 

 form of a sharp ridge. 



Third radials five; pentagonal; broader than high; same size, or- 

 namented near their center by a knob. 



Secondary radials, first series ten of irregular form ; as large as or 

 larger than the third primary radials; principally hexagonal — some- 

 times one or more are pentagonal. 



Secondary radials, second series, varying in number from ten to thir- 

 teen; irregular in form and size. Inter axilary pieces; these pieces 

 are variable, differing in form and size, and are distinguished as trian- 

 gular and quadrangular — the triangular pieces having their origin in 

 the radial pieces ; eight in number ; those originating from the inter- 

 radial piece of the second series are quadrangular ; twelve or more in 

 number. 



Interradials five ; very large; nonagonal ; angularly pointed below ; 

 truncated on the superior margin ; from these rise the secondary ra- 

 dials, five in number, four of which are pentagonal ; pointed at the 

 summit ; inferior margin as wide as the superior margin of the first 

 interradials on which they rest ; the other piece is quadrangular. 



The arms are ten in number, rising in pairs ; rather short ; tapering 

 rapidly ; composed of ovoid flat pieees, of equal thickness — one side 

 exhibiting the articulating surfaces from which tentaculse have been 

 detached ; the form and arrangement of the tentaculse are unknown. 



Summit. The summitis covered by ratherlarge polygonal pieces, va- 

 rious in form ; generally ornamented by small granular prominences. 



Proboscis or oral tube. In its complete form it is unknown ; judg- 

 ing from the fragments found attached to the specimens, it is small com- 

 pared with the same appendage in other crinoids ; composed of small 

 polygonal pieces. 



