1890.] NATURAL SCIENCES OF PHILADELPHIA. 363 



the rays were perisomic. We arrived at this conclusion after dis- 

 covering that the interradials of the Camerata are continued into 

 the " vault," and supposed that underneath them there was another 

 system of skeletal plates which, like the former, extended from the 

 upper margin oftlieradkds up to the orals. It was upon these grounds 

 that we held the iuterradial plates of Apiocrinus and Guettardi- 

 criims to be enormously developed perisomic plates, and upon the 

 same piincij)le we called the corresponding plates in the Ichthyo- 

 crinidae perisomic, as soon as we had found an open mouth and a 

 true disk in Taxocrinus. The " calyx interradials," we thought, 

 formed an upward prolongation of the dorsal cup, and the perisomic 

 plates a downward extension of the disk, as was practically done by 

 Carpenter in the case of thePentacrinidae and Comatulidae, and in 

 the Palaeozoic Reteocrinidae and Platycrinidae ; while in other groups 

 he seems to have been of the opinion that the " calyx interradials " 

 are followed sometimes by vault — and sometimes by disk plates. In 

 Thaumatocrinus he calls the large plates between the radials " calyx " 

 interradials, and the smaller ones above perisomic plates. In Glypto- 

 crimis it appears that he regarded the plates between the rays as 

 " calyx " interradials and those of the dome as perisomic. In the 

 Actinocriuidae, however, he thought the " calyx " interradials to be 

 followed by a vault. All this indicates that in these groups Car- 

 penter was influenced largely, if not altogether, by the size of the 

 plates and their regular or irregular arrangement. He regarded 

 the plates as " calyx " interradials and vault pieces, respectively, 

 when large and regularly arranged, but as perisomic plates when 

 small and of ill-formed boundaries. We allude to these facts 

 to show that neither the small size of the plates, nor the pres- 

 ence of ambulacra upon the surface, are good criteria to make 

 them perisomic plotes. That there exists, however, a close re- 

 semblance in some of these forms with some of the perisomic plates 

 of recent Crinoids, we are quite ready to admit, and in pointing this 

 out. Dr. Carpenter, no doubt, laid the foundation for a better under- 

 standing of those structures ; but he did not go far enough. He 

 overlooked that among palaeozoic and recent Crinoids are found 

 all intermediate stages from the membranous disk of Antedon 

 to the solid vault of an Actinocrinus or Batocrinus, and this fact has 

 led us to enquire whether all interradial and " vault " plates are not 

 perisomic. 



