1869.] MEEK AND WORTHEN — ON PALEOZOIC CRINOIDEA. 443 



stand with its middle almost, but apparently not exactly, under 

 the middle of the nearly central proboscis of the vault ; while at 

 the anterior side of its upper margin, and a little out from under 

 the proboscis, it shows remains of a kind of thickened collar, 

 which we found to be composed of minute calcareous pieces. 

 From this there radiate five ambulacra, compo-ied of the same 

 kind of minute pieces as the collar itself, each ambulacrum 

 consisting of two rows of these minute pieces alternately arranged. 

 They are each also provided with a distinct furrow along their 

 entire length above. As they radiate and descend from their 

 connection with the top of the convoluted frame-work of the 

 digestive sack, they all bifurcate, so as to send a branch to each 

 arm-opening, those passing to the posterior rays curving a little 

 at first above, so as not to pass directly under the proboscis. 

 These ambulacra, although passing along obscure furrows in the 

 under side of the vault, which are deepest near the arm openings, 

 are not in contact with the vault, or visibly connected with any 

 other parts than the top of the convoluted digestive sack, and the 

 outer walls at the arm-openings. Each of their sub-divisions can 

 be traced into an arm-opening, and it is very probable that thev 

 continued out on the ambulacral furrows of the arms and tentacula. 

 At one point in one of theso ambulacral canals, beneath the vault, 

 some evidences of the remains of two rows of minute pieces were 

 observed alternating with the upper edges of those composing the 

 under side of these canals, and thus apparently covermg them 

 over. The condition of the parts is such, however, as scarcely to 

 warrant the assertion that this was really the case, though we are 

 much inclined to think it was. If so, these canals must have 

 been, at least under the vault, hollow tubes, formed of two rows 

 of pieces below, and two above, all alternately arranged. 



We are not aware that any evidences of the existence of these 

 delicate ambulacral canals, composed of minute calcareous pieces, 

 and passing beneath the vault from the arm-openings to the 

 summit of the convoluted digestive sack, have ever before been 

 observed in any Crinoid, recent or extinct; and we can but think 

 it probable, that the extremely rare combination of circumstances 

 that brought them to light in this instance may not again occur 

 for centuries to come, with regard to another specimen. That 

 they correspond to the ambulacral canal seen extending from the 

 arm-base to the mouth, on the outside of the ventral disc in 

 Comatula, is clearly evident. 



