248 Cincinnati Society of Natural Histonj. 



the body became smaller; the degree of definiteness in the al'eas l)ecame 

 less; and finally the whole system of plates iiuited, arching over the 

 bod}^ cavity, and forming what our collectors have long known as the 

 " stomach" of Olyptocrinus. At this time the rays became free arms, 

 and the ambulacral grooves were now carried by them outside the body 

 cavity. These grooves, in the G. onealli at least, were covered in by 

 a series of plates attached to the edges of the arms, between which 

 and the latter, the pinnulse passed out. These plates become less and 

 less developed from the inner bases of the arms outward, and disap- 

 pear before reaching the tip of the latter. In the same species both 

 grooves and pinnulas are continued into the ra^'S beneath the vault or 

 covering of the body. On account of its position as an intermediate 

 link, very great interest attaches to this species, and collectors in its 

 horizon should search diligently for every scrap of evidence concern- 

 ing it, as well as its not less interesting relative, the Gr.fomshelU. 



Cromyockinds gracilis, nov. sp. 



Plate XVI., fig. 2, basal ; 2a, azygos ; 25, opposite side ; 2c, view of ventral tube ; Id, in- 

 side view of arm with pinnulae ; 2c, inside view of arm without pinnulaj. 



Under basals — Five, pentagonal as seen from the outside, lying at 

 the base of the columnar depression, and ver}^ rarely exhibited in any 

 of the specimens. They are wider than high, and their apices are on 

 a line with the junction of the first sub-radials. 



Basals — Five, three pentagonal, the two on the az^'gos side hexag- 

 onal. The three pentagonal plates are pointed at the upper extremity, 

 which is continuous with the line of junction of the contiguous first 

 radials, the lower sides of which rest upon the upper, sloping faces of 

 these plates. 



The two hexagonal sub-radials are made so by the truncation of 

 their angles for the support of the azygos plates. The one on the 

 right has its inner middle angle truncated for the support of the lower 

 end of the lowest right hand plate of the azygos series, as ma^- be seen 

 in the figure. The one on the left, or the adjacent sub-radial on the 

 same side, has its upper central angle truncated for the support of 

 the lower left hand plate of the az^^gos series. All these plates are 

 convex exteriorly, and so folded in below as to form the columnar 

 depression, at the bottom of which the small basals may be seen. 

 The3^ are without ornamentation. 



JRadials — First series five, wider than high, pentagonal, all having 

 a broad articulating face above, upon which rest the radials of the 



