328 PROCEEDINGS OF THE ACADEMY OF 



conspicuous, and we had never entertained any other opinion in regard to 

 them, than that they are the only passages of communication that could have 

 existed between the softer parts occupying the ambulacral furrows of the arms, 

 ■and the interior of the body, Mr. Billings was the first author, so far as we 

 are at this time aware, who called especial attention to them in this regard. 

 We regret that we have not space to quote a portion, at least, of his remarks 

 on this subject, and would advise the student to read attentively the whole of 

 both of his articles alluded to. 



The specimens at Mr. Billing's command enabled him to trace the courses of 

 the ambulacral canals from the arms, through the walls of the body at the 

 arm-bases, and to ascertain the additional fact that, after passing through the 

 walls, they seemed to have turned upward ; but beyond this he had not the 

 means of tracing them farther. 



A single specimen of Aclinocrinus proboscidialis, however, in Mr. W^a.chsmuth'3 

 collection, is in a condition (thanks to the great skill of that gentleman, and 

 the exceedingly fortunate state of preservation, by which its delicate internal 

 parts remain almost entire, and without any surrounding matrix) to throw 

 much additional light on this subject. By very dextrous manipulation, Mr. 

 Wachsmuth succeeded in removing about half of its vault, so as to expose the 

 internal parts, in place, and in an excellent state of preservation. The convo- 

 luted 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 de- 

 tached 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 en- 

 tirely free from any inorganic incrustation. Its slightly dilated upper end 

 seems to 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 re- 

 mains 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 ra- 

 diate 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 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 war- 

 rant 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 alter- 

 nately 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 oljserved in any Crinoid, recent or extinct; and we can 

 but think it probable, that the extremely rare combination of circumstances 



[Dec. 



