FOSSILS OF THE BURLIXGTOX GROUP. 331 



which its delicate internal parts remain almost entire, and without any 

 surrounding matrix.) to throw much additional light on the subject. 

 By very dextrous manipulation, Mr. WACILSMUTH succeeded in remov- 

 ing about half of its vault, so as to expose the internal parts, in place, 

 and in an excellent state of preservation. The convoluted organ already 

 described in other species is in this comparatively large, subcylindrical 

 in the middle, apparently tapering at the lower end, and a little dilated 

 at the upper extremity. It seems to be rather dense, and shows the 

 usual rough appearance, but as we had no opportunity to examine any 

 detached fragments of it by transmitted light, we did not determine 

 whether or not it has pores passing through it, though it probably has, 

 at least when entirely free from any inorganic incrustation. Its slight- 

 ly dilated upper end seems to stand with its middle almost, but ap- 

 parently 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, composed 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 pro- 

 boscis. These ainulacra, 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 subdivisions can be traced into an 

 arm opening, and it is very probable that they continued on out the 

 ambulacral furrows of the arms and tentacula. At one point in one 

 of these 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 covering 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 deli- 

 cate ambulacral canals, composed of minute calcareous pieces, and 

 -ing l>eneath the vault from the arm openings to the summit of the 



