0. P. Keyes — Sedentary habits of Platyceras. 271 



gasteropods and their associated crinoids is taken into consider- 

 ation, for there was presumably no very great difference in the 

 habits of the living and their closely allied fossil species. And 

 it is known that living crinoids subsist chiefly upon animalcules 

 and microscopic plants, and that the food of most, if not all, of 

 the Calyptrceidce is of a similar nature. 



The extensive crinoidal collections of Mr. Charles Wachs- 

 muth contains numerous examples of palseocrinoids with 

 attached Platycerata, an examination of which has fully and 

 satisfactorily corroborated many of the observations of Meek 

 and Worth en. The species examined were chiefly Arthroa- 

 cantha punctobrachiata Williams, Ollacrinus tuberosus Lyon 

 and Cassidy, 0. typus Hall, Platycrinus hemisphericus Meek 

 and Worthen, Physetocrinus ventricosus Hall, Actinocrinus 

 (sp.?). It will be noticed that in the genera to which the first 

 five species belong the vault is very much depressed or almost 

 flat and the ventral aperture is a simple opening ; while in the 

 last genus the ventral opening is situated at the extremity of a 

 prolonged '-proboscis." In nearly every case observable the 

 Platyceras completely covers the opening in the vault and this 

 fact has led many of the earlier writers to suppose that the 

 crinoid was feeding upon the Platyceras when it perished; it 

 has also suggested that the Platyceras may have fed in part at 

 least upon the excrementitious matter from the crinoid. In 

 the case of Actinocrinus, the Platyceras was attached to the 

 vault at the base of the " proboscis," and was nearly hidden 

 from view by the arms of the crinoids. Meek and Worthen 

 have pointed out* and it is clearly observable in nearly all the 

 examples examined, that the attachment of Platyceras to the 

 various species of crinoids is not the result of accidental pres- 

 sure but that it was acfually attached during life, as is shown 

 by the sinuosities in the lip of Platyceras corresponding ex- 

 actly to the irregularities of the surface to which the shell was 

 attached. Of the Crawfordsville species Platycrinus hemi- 

 sphericus and Ollacrinus tuberosus when having Platyceras 

 attached, Platyceras infundibulum M. and W. is usually 

 associated with the former and P. cequilatera with the latter. 

 In the absence of direct proof to the contrary this has led 

 Meek and Worthen to suggest that " it is worthy of note that 

 it is always a sub-spiral Platyceras that we find attached to this 

 crinoid (0. tuberosus) so that here at least it would seem that 

 each of these crinoids has its own particular species of Platy- 

 ceras" The recent examination of an extensive series of both 

 of these species has disclosed in a number of instances the 

 occurrence on Platycrinus hemisphericus of Platyceras cequi- 

 latera instead of the more common Platyceras infundibulum / 



* Geol. 111., vol. iii, p. 386. 



