P ILffiONTOLOOICAL REPORT OP GEOLOGICAL SURVEY. 489 



one of the hex agonal pieces. The bending or angular deflection of 

 these pieces, into the columnar-pit, is most remarkable, forming, as 

 they- do, a margin about equal to their thickness around the external 

 margin of the columnar-pit, around the column presenting the appear- 

 ance as if their junction with the first primary radials was against 

 their inner face, and not by the inferior margin of the pieces, as is 

 usually the case with crinoidea. The sides of the pieces or branches 

 of the forks are nearly of equal width, tapering or curving slightly 

 from within the. fork outward; the lateral margins are straight; their 

 summits are variously truncated, sometimes by a straight line from 

 within the fork outward and downward; again, by an additional corner re- 

 moved from the point within the fork, and sometimes they are found irre- 

 gularly rounded from the center of the branches to either side; all these 

 forms are seen in a single specimen. The angular indentation between 

 the branches of the fork terminates in a prominent cup, from which pro- 

 ceeds, upward, on either branch of the fork, defining the space between 

 them, a sharp prominent margin marking the limit of the branches of 

 the fork. The branches of the second primary radials are also marked 

 with lines of increment, which conform to the upper and outer margins 

 of the pieces. The lines are prominent, and are probably the remains 

 of the processes marking the margins of the pieces above alluded to. 



Interradial pieces — (No. 4, fig. 1, plate v.) These five pieces are 

 long, (seven times as long as their greatest width;) lanceolate, rising 

 from the notched and curved superior margins of two adjacent branches 

 of the second primary radial pieces, and terminating at the summit of 

 the body, between the ovarial (?) openings; they are divided longi- 

 tudinally by a line from which fine depressed striae diverge at an angle 

 of abont 60° (upward and outward,) dividing the parts of the piece on 

 either side of the center line into flat bands, equal in width to the ribs 

 on the pieces on either side of the pseudambulacral fields, and the 

 pieces composing these, the ambulacrse — sixty of which are contained 

 in an inch* 



The parts here designated interradial pieces, in the best preserved 



* Dr. Roemer's figure represents this part, which is the middle of his "deltoid pieces," as 

 covered with punctures, ("chayrinartig bedect." ) In the above description this part is called 

 interradial piece, and is separated from the pseudambulacral fields, and from the spaces on either 

 side of them. In no specimen, Of thousands, has this punctured surface been observed; it is 

 probably the effect of cleaning with a pointed instrument. It has been observed in some so 

 clean ed. 



62 



