330 PALAEONTOLOGY OF ILLINOIS. 



older types, and that of the few living examples of this extensive order 

 of animals. That is he noticed the facts that while in the living Coma- 

 tula and PentacrimtSj the ambulacral canals "are seen extending from 

 the arm-bases across the surface of the soft skin-like ventral disc, to 

 the central mouth, and these genera are provided with a separate anal 

 opening, situated excentrically between the mouth and the posterior 

 side, tha^t in the Palaeozoic Crinoids the ventral disc is very generally, if 

 not always, covered by close-fitting, solid plates, showing no external 

 traces whatever of ambulacral furrows extending inward from the arm- 

 bases ; and that in nearly all cases they are merely provided with a 

 single excentric, or subcentral opening, often produced into a long tube 

 which, like the vault, is made up of solid plates. He showed that there 

 is no evidence whatever that the ambulacral canals in these older types 

 were continued along the surface of the vault from the arm bases to 

 the only opening, whether subcentrally or laterally situated, and that 

 in cases where this opening is produced in the form of a greatly elong- 

 ated proboscis, or tube, such an arrangement of the ambulacra would 

 be almost a physical impossibility. Hence he concluded that the ambu- 

 lacral canals must have passed directly through the walls of the body 

 at the arm-bases ; and he gave several figures of various types, show- 

 ing openings at the base of the arms, through which he maintained 

 that the ambulacra must have passed to the interior of the body from 

 the arms. 



Although these arm openings had long been well known to all fa- 

 miliar. Avith our numerous types of western Carboniferous Crinoids, in 

 which they are very 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. BILLINGS' 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. 



A single specimen of Actinocrinus proboscidialis,* however, in Mr. 

 WACHSMUTH'S collection is ijj a condition (thanks to the great skill of 

 that gentleman, and the exceedingly fortunate state of preservation, by 



*Plate 0, Fig- 8. 



