446 THE CANADIAN NATURALIST. [DeC. 



know, the anibulacral canals were so highly developed under it 

 i'rom the arm-openings to the entrance into the top of the alimen- 

 tary canal ? Indeed it seems at least probable, that if the soft 

 ventral disc of Comatula had possessed the power of secreting 

 solid vault-pieces, as in most types of Palaaeozoic Crinoids, that 

 these vault-pieces would not only have covered over the ambulucral 

 furrows, as in the Palaeozoic types, but that they would also have 

 hermetically cov>n-ed over the mouth, and converted the little 

 flexible anal tube into a solid calcareous pipe, such as that we 

 often call the proboscis in the extinct Oinoids. 



From all the facts, therefore, now known on this pi)int, 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 posterially, sub-centrally, 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 ond 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 

 throush the vault ? 



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

 objection may bo urged against this suggestion, and in favour of 

 the conclusion 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 i'alae ;zoic species, with the shell of a Platjjceras 

 in close contact by its aperture, either with the side or the vault 

 of the Crinoid, and not unfrequently actually covering the only 

 opening in the vau t of the latter, so as to have led to the opinion 

 that the Crinoid was in the very act of devouring the Mollu.^k 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. 

 hcriiisphcerlcns), 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 Plati/ctras (/*. 



