334 PALAEONTOLOGY OF ILLINOIS. 



flexible aiial tube into a solid calcareous pipe, such as that we often call 

 the proboscis in the extinct Crinoids. 



From all the facts, therefore, now known on this point, we are led to 

 make the inquiry : whether or not, in all the Palaeozoic Crinoids in 

 which there is but a single opening in the vault whether it is a simple 

 aperture, or prolonged into a proboscis, and placed posterally, subcen- 

 trally, or at some point on a line between the middle and the posterior 

 side this opening was not, instead of being the mouth, or both mouth 

 and anus, as supposed by some, really the anal aperture alone ; and 

 whether in these types the mouth was not generally, if not always, 

 hermetically closed by immovable vault pieces, so far as regards any 

 direct opening through the vault 1 



We are aware of the fact that at least one apparently strong objec- 

 tion may be urged against this suggestion, and in favor of the conclu- 

 sion that the single opening seen in these older Crinoids was the mouth, 

 or at least performed the double office of both anal and oral aperture. 

 That is, the frequent occurrence of specimens of these palaeozoic species, 

 with the shell of a Platyceras in close contact by its aperture, either 

 with the side or the vault of the Criuoid, and iiot.tmfreqiientl y actually 

 covering the only opening in the vault of the latter, so as to have led to 

 the opinion that the Crinoid was in the very act of devouring tbe Mol- 

 lusk at the moment when it perished. 



Amongst the numerous beautiful specimens of Crinoids found in the 

 Keokuk division of the Lower Carboniferous series at Crawfordsville, 

 Indiana, there is one species of Platycrinus (P. hemisphcericitsj, that is 

 so abundant that probably not less than two hundred, and possibly 

 more, individual specimens of it have been found there by the different 

 collectors who have visited that noted locality ; and, judging from those 

 we have seen, apparently about one half of these were found with a 

 moderate sized, nearly straight, or very slightly arched and conical 

 Platyceras (P. infundibulumj, attached to one side by its aperture, 

 between the arms of the Crinoid and often so as to cover the single 

 lateral opening in the vault of the same.* From the direction of 

 the slight curve of the apex of the Platyceras, it is also evident that 

 it is always placed in such a manner, with relation to the Crinoid, 

 that the anterior side of the Mollusk was directed upward, when 



* We at one time thought these shells attached to the side of this Platycrinus, to be out of reach of 

 the opening, or supposed mouth, because we had not seen specimens showing the position of the open- 

 ing in this species, and had supposed, from its .similarity to I'lafi/frinux ymintlatiix. Miller, and other 

 species without a lateral opening, that such was also the case with this. We have since seen speci- 

 mens, however, showing that it has a lateral opening, and therefore belongs to the group Pleurocri- 

 nus; so that it is probable these shells often cover this opening. See PI. 16, Fig. 6, a, b. c. 



