6 Cincinnati Society of Natural History. 



the vault of many specimens is capped either b}' a Mollusc,* or by a 

 pentagonal plate. In the best preserved specimens, this plate has five 

 carinated ridges radiating from a point on the az3-gos side of the cen- 

 ter, and terminating in rounded protuberances at the peripheral angles, 

 the two hang on each side of the azygos face being the largest. The 

 bases of the interbrachial rays abut upon these protuberances, the 

 upper side of the plate lying somewhat below them. The sides of this 

 plate are slightl}^ excavated between the five angles, ihp deepest exca- 

 vation being on the azygos side. On breaking away one of the Gas- 

 teropods, I found the aperture of the shell to be applied over the upper 

 end of the vault, and that the terminal plate was in position at its apex. 

 In specimens not covered by these shells, it can be seen that the small 

 lateral, terminal plates of the vault were not perforated, but there are 

 evidences that the under side of the cap-piece was radially excavated,the 

 excavations being indicated by the carinated ridges mentioned above; 

 so that, if any summit openings existed, they must have been under 

 the edges of the pentagonal cap-piece. These openings may be seen 

 excavating the under surface of the protuberances at the angles of the 

 cap-piece. It thus appears that the only openings of this Crinoid were 

 those communicating with the ambulacral grooves of the arms, the 

 anal (?) opening, and those at the apex of the A'ault. The inside of 

 the plates of the vault and pelvis, gives no evidence of processes 

 for the attachment of au}^ skeletal framework, and it is probable that 

 any such apparatus as it may have contained was membranous and 

 perishable. It is also likely that ciliary currents, having entered the 

 vault by the perforations at the base of the ambulacral grooves, were 

 expelled by the openings at its summit, as there is a canal leading 

 downward from beneath the cap-piece, and gradually increasing in 

 size as the vault enlarges towards its base. The sj^stems of radiating 

 vessels so often traceable in many other Crinoids, are here represented 

 only by the arm-furrows and the perforations of the vault, so far as at 

 present determined. 



The Interbrachial Rays. 

 Of these there are five, which are either spatulate, claviforni, or 

 cuneiform, with many variations of these ty[)es. In some of the 

 species they are thin and knife-like throughout their length; in others, 



* About one half of the spociinens found have the top of the vimU coverod by a small 

 species oi PlatycevaK. A larger species is frequently found attached to the pelvis of /^/i/^y- 

 crinus heminphericun, in such a way as to cover the azygos area. These Molluscs were evi- 

 dently parasitic on the Crinoids, as the edges of the shells have so grown in position as to 

 accommodate themselves to the sinuosities of the surfaces upon which they rest. It is 

 more than proliahle that they fed upon the exuviiO of the Crinoid. At all events, the 

 most perfect vaults yet found are those covered ))y these shells. Attention has been called 

 to tills subject by Prof Worthon, and it is certainly worthy of more careful examination. 



