Summit Structure of Pentremites. 489 



site the middle of the plates of the other series. No indi- 

 cations of ciliated appendages to the tentacula have been 

 observed. 



Observations on certain modifications of the structure of 

 the probosces of Actinocrinus. 



Although the Carboniferous limestones of the West have 

 yielded such great numbers of crinoids in a good state of 

 preservation, belonging to numerous genera and species, 

 it is to be regretted that so little light has been thrown 

 upon their animal economy, in addition to that which has 

 long been known. 



Most fossil crinoids evidently possessed but a single 

 opening,* usually called the anal aperture, yet separate 

 anal and buccal apertures and tubes have been noticed by 

 European authors, but so far as I am aware, the following 

 are the only instances of their recognition in specimens 

 from American strata, if we except the Blastoidea, which, 

 however, should not be excepted in all cases, if the con- 

 clusions recorded on a previous page are correct. 



A specimen of an Actinocrinus, apparently A. Verneuilia- 

 nus of Shumard, shows two strong plated tubes, each hav- 

 ing the structure of the proboscis of Actinocrinus, protrud- 

 ing from each side of the mass of its folded arms. To 

 make sure that the connection between them was com- 

 plete, the specimen was ground off so as to show the 

 junction in the most perfect manner. 



The height of the body to the base of the proboscis is 



* That the single aperture of Platycrinus and other genera contained both the 

 buccal and anal openings there can be no question. The apparent inconvenience 

 of such an arrangement is shown by the not uncommon discovery of the shell of 

 a Platyceras, inverted over the aperture, closely clasped by the arms of the cri- 

 noid, which had evidently died before devouring the contents of the shell. If the 

 animal had lived to consume the food thus secured, the shell would certainly have 

 been much in the way of a proper performance of other functions. The idea that 

 the Gasteropod was the attacking party seems untenable, from the fact that the 

 famUy are all regarded as vegetable feeders. 



JOURNAL B. S. N. H. 62 JANUARY, 1863. 



