166 GASTBROPODS. 



part sinuous or crenate. In the absence of salient classtfica- 

 tory characters these features were regarded usually of much 

 importance for specific distinction. It was not until a compar- 

 atively recent date that their true significance was indicated. 

 The fact here referred to is the attachment of fossil Oapuli to 

 foreign bodies, and particularly to the calyces of crinoids. The 

 observations on this habit of the ancient Oapuli have been fully 

 considered elsewhere, but may be here briefly summarized by 

 stating that in all the examples examined upward of several 

 hundreds (1) the gasteropod shell invariably lies over the anal 

 opening of the crinoid ; (2) the mollusk remained in this posi- 

 tion for a considerable period, probably for the greater part of 

 life, as is shown by the shells on highly-ornamented calyces, 

 and by the removal of them from their places of attachment, 

 and tracing the growth of the shell by the concentric grooves 

 made on the ventral plates; (3) -the growing shell followed 

 closely the inequalities of the surface upon which it rested 

 depressions giving rise to furrows and protuberances to folds 

 or nodes ; and (4) shells simply lying on flat surfaces are much 

 more depressed and proportionally broader than those clinging 

 to the vertical or inclined portions of calyces where the anal 

 opening is situated laterally. The third of these statements is 

 perhaps best illustrated by crinoids having low interradial areas 

 and elevated radial regions ; and this is the probable explana- 

 tion of the frequent occurrence of the more or less distinctly 

 five-lobed calyptraean shells. Heretofore this phenomenon has 

 admitted of no direct causal interpretation. 



Attachment to Grinoids. The adherence of gasteropods of 

 the genus under consideration to fossil crinoids was at first 

 thought to furnish conclusive evidence of the carnivorous hab- 

 its of the Orinoidea; and inasmuch as it was at that time con- 

 sidered that the aperture in the vault was the mouth, this 

 explanation seemed very plausible. Consequently, the conclu- 

 sion was very naturally reached that the crinoid, when it per- 

 ished, was in the act of devouring the mollusk. Meek and 

 Worthen appear to be the first to question the prevalent opin- 

 ions regarding the intimate association of crinoid and gastero- 



