PALEONTOLOGY OF ILLINOIS. 



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 circnmstanc.es 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 

 canals seen extending from the arm-base to the month, on the outside 

 of the ventral disc in Comatula, is clearly evident. 



The presence of furrows radiating from the central region of the 

 under side of the vault to the arm openings, in various types of Palseo- 

 zoic Crinoids, must have been frequently observed by all who have had 

 an opportunity to examine the inner surface of this part. Messrs. 

 DE KONINCK and LEHON figure a portion of the vault of Actinocrinux 

 stellaris, in their valuable Eeclierches sur les Crinoides du Terr. Garb, de 

 la Belgique, pi. 3, fig. 4 f. , showing these furrows, which they seem to 

 have regarded as the impressions left by the muscles of the viscera. 

 The inner surface of the vault of most of our western Carboniferous 

 Crinoids is known to have these furrows more or less defined, either 

 from specimens showing this inner surface, or from natural casts of the 

 same. In some instances they are very strongly defined from the 

 central region outward to the arm bases, to each of which they send a 

 branch. In Actinocrinus ornatus, Hall, for instance, they are gener- 

 ally so strongly defined as to raise the thin vault into strong radiating 

 ridges, separated by deep furrows on the outer side. In 8trotocrinu8, 

 the vault of which is greatly expanded laterally, and often flat on the 

 top, these internal furrows, in radiating outward, soon become sepa- 

 rated by partitions, and as they go on bifurcating, to send a branch to 

 each arm, they actually assume the character of rounded tubular canals, 

 some distance before they reach the arm-bases. 



That these furrows or passages of the inner side of the vault were 

 actually occupied during the life of the animal by the ambulacral 

 canals as they radiate from the top of the convoluted digestive sack to 

 the arm openings, we think no one will for a moment question, after 

 examining Mr. WACHSMUTH'S specimen of Actinocrinm proboscidi-alis* 

 which we have described, showing all these parts in place. It is also 

 worthy of note that in all the specimens of various types in w r hich these 

 furrows of the under side of the vault are well known, whether from 

 detached vaults or from casts of the interior of the same, they never con- 

 verge directly to the opening of the -vault, but to a point on the anterior side 

 of it, whether there is a simple opening or a produced proboscis. The 

 point to which they converge, even in types with a decidedly lateral 

 opening of the vault, is always central or nearly so, and even when the 

 opening is nearly or quite central, the furrows seem to go, as it were, 



* See PI. 9, Figs. 7, 9 au<l 10. 



