88 PROCEEDINGS OF THE ACADEMY OF 



is never situated at the point of convergence of the ambulacral canals, where 

 the mouth ought to be, but more or less removed from it, so that if it per- 

 formed both the offices of mouth and vent, it would be, as it were, the anal 

 opening that did so, instead of the mouth, as in all of those cases among the 

 existing Echinodermata with but one opening to perform both functions. In 

 addition to this, we have, as we believe, demonstrative evidence that species 

 of I'latycrinus and Goniasteroidocrinus could, and did live, in some way, with 

 the only opening (excepting the arm-openings) covered by a Plaiyceras that 

 grew there, and sometimes not only so as to cover the opening, but in the case 

 of the Goniasteroidocrinus, so as to cover nearly the whole vault. That these 

 shells did not merely grow upon dead Crinoids lying at the bottom of the sea, 

 is evident from the fact that these Crinoids thus found in such numbers, with 

 a Platycems attached, at Crawfordsville, always have the arms and most deli- 

 cate pinnulae perfectly preserved ; and in some other instances where the 

 Plaiyceras is attached to the top of the vault, the arms of the Crinoid are found 

 folded over the shell, as they would naturally fold together by the contraction 

 of the muscles at death. Had these Crinoids remained uncoved by sediment 

 at the bottom of the sea long enough after death for the Plaiyceras to grow 

 upon them, their arms and pinnulse would have fallen to pieces. If the only 

 opening in the vault ©f these Crinoids was the vent only, we could readily 

 understand how the excrementitious matter might have escaped under the foot 

 of the Plaiyceras ; but if it was both mouth and vent it is difficult to under- 

 stand how, in such a case, food could have passed in. 



Again, in many of the Actinocrinida, the only opening in the vault (except- 

 the arm-openings) is situated at the extremity of a long, slender, straight tube, 

 rising from near the centre of the vault, though never from directly over the 

 point of convergence of the ambulacral canals. And it is a remarkable fact, 

 that of the hundreds of specimens we have seen with more or less of this tube 

 preserved, we have never yet seen one that had its extremity unbroken. In 

 several instances we have seen it from one to three inches in length, and so 

 attenuated in the latter cases, that the internal cavity was not more than 0-05 

 inch in diameter, even in large specimens ; and in others we have seen it scarce- 

 ly more than one hundredlh of an inch in diameter, and still the end of the tube 

 in all cases broken. How small this canal must be at the end of an unbroken 

 tube, we cannot say, but it must evidently be very small. If this little pore- 

 like opening, situated at the extreme end of this long, straight, rigid tube, 

 performed the functions of both mouth and vent, it would certainly seem to 

 be a very unnatural and inconvenicHt structure. 



In regard to the internal convoluted organ seen in so many of the Actino- 

 cridie belonging to the respiratory instead of the digestive system, we would 

 remark that its large size seems to us a strong objection to such a conclusion. 

 In many instances it so nearly fills the whole internal cavity that there would 

 appear to be entirely inadequate space left for an organ like a digestive sack, 

 outside of it, while the volutions within would preclude the presence of an in- 

 dependent digestive sack there. In addition to this, the entire absence, so far 

 as we can ascertain, of any analogous, internal respiratory organ in the whole 

 range of the recent Echinodermata, including the existing Crinoids, would appear 

 to be against the conclusion that this is such, unless we adopt the conclusion 

 of Dujardin and Hupe, that the Palteozoic Crinoids had no internal digestive 

 organs, and were nourished by absorption over the whole surface. We should 

 certainly think it far more probable that this spiral organ is the digestive sack, 

 than a part of a respiratory apparatus. 



Genus GRANATOCRINUS, Troost. 



Granatocrinos melonoides, M. and "W. 



Body rather under medium size, globose in form. Base very small, nearly 

 even with the prominent lower extremities of the pseudo-ambulacral areas. 



[April, 



