448 THE CANADIAN NATURALIST. [DeC. 



In all of these, aud numerous other examples that might be 

 mentioned, it is worthy of note that it is to species of Crinoids 

 with a simple openiug in the vault, and not to any of those with 

 a produced proboscis, that we find these shells attached in this 

 way ;* and it is so rarely that we find shells of any other genus 

 than Pldtyctras, apparently attached to, or in contact, with the 

 body of a Crinoid, that it seems probable where other shells are 

 occasionally so found, that their connection with the Crinoid may 

 be merely accidental. If it could be established as a fact, that 

 these Crinoids were actually devouring these Molluscs, by 

 sucking out, or otherwise extracting and swallowing their softer 

 parts, in any instance where they have been found with a shell 

 attached over the opening of the vault, this would, of course, 

 establish the fact that this opening is the mouth, or, at least, that 

 it must have performed the office of both oral and anal aperture. 

 But to say nothing in regard to all that is known of the habits 

 and food of the recent Crinoids being so directly opposed to such 

 a conclusion, the fact that so large a proportion as nearly one-half 

 of all the individuals of some species should have died at the 

 precise moment of time when they were devouring a Plati/ceras, 

 and should have been imbedded in the sediment and subsequently 

 fossilized without separating from the shell, seems, to say th^ 

 least of it, very improbable. 



And it is even more difficult to understand upon what principle 

 an animal with its viscera incased in a hard unyielding shell, 

 composed of thick, close-fitting calcareous pieces, and with even 

 its digestive sack, as we have reason to believe, at least to sonie 

 extent, similarly constructed, could have exerted such powers of 

 suction as to be able to draw out and swallow, through an 

 aperture in its own shell, often less than one-tenth of an mch in 

 diameter, the sotter parts of a moUusk nearly or quite equal in 

 volume to the whole of his own visceral cavity. hat they ever 

 did so, however, becomes still more improbable when we bear in 

 mind the fact, that the animal supposed to have performed this 

 feat, lived, at least during the whole of its adult life, attached to 

 one spot by a flexible stem, that only allowed it a radius of a 

 foot or so of area to seek its prey in ; while the mollusc it is 

 supposed to have so frequently devoured, from its close affinities 



♦Possibly due to the fact, that in species with a proboscis there is 

 much less room for attachment to the vault. 



