1885.] NATURAL SCIENCES OP PHILADELPHIA. 293 



the calyx is almost always disturbed by a greater or less modi- 

 fication of the plates on the anal side." 



5. In the Neocrinoidea "the basals are pierced by interradial 

 canals or grooves, which lodge the cords proceeding from the 

 angles of the chambered organ," whence they pass into the 

 radials. None of them have permanently imperforate radials as 

 so many Palaeocrinoidea, the latter group remaining in an embry- 

 onic condition. 



6. In the Neocrinoidea, with the exception of Metacrinus and 

 Plicatocrinus, the axillary is the third of the primary radials ; 

 while in the Palaeocrinoidea the first radials themselves may be 

 axillary or any other plate bej^ond the first. 



7. The arms of the Neocrinoidea, with the exception of one or 

 two species of Encrinus, are uniserial, those of the Palaeocrinoidea 

 frequently biserial. 



8. The mouth and food grooves of all adult Neocrinoidea are 

 exposed to view ; in the Palagocrinoidea, with but few exceptions, 

 closed by plates. 



In most of these points we agree with the English scientist, 

 but in some of them we think modifications should be made, and 

 there is one point to which he did not give the importance which 

 we think it deserves. 



We agree with Carpenter that underbasals are rarely observed 

 in Neocrinoids, which, as we have stated elsewhere, are built 

 upon the plan of dicyclic Crinoids. The angles of the column 

 are directed interradially, the cirrhi radially; while the opposite 

 is the case in Actinocrinus, Glyptocrinus, Belemnocrinus, Hetero- 

 crinus, etc., which are known to be monocyclic, and we conclude 

 from this structure that all Neocrinoidea, or at least most of 

 them, in their larval state may have possessed rudimentary 

 underbasals hidden by the column. 



Among Neocrinoidea, Thaumatocrinus is the only genus in 

 which calyx interradials are evident, and it is very doubtful to us 

 whether even these plates, which rest within the ring of the first 

 radials, really are the homologues of the first interradials of the 

 Actinocrinidse, Platycrinidas or Cyathocrinidae. The interradials 

 of Thaumatocrinus were covered in the larva by the oral pyra- 

 mid ; while those of the young Palaeocrinoid form the whole of 

 the ventral surface. The so-called " interradials " of Guettardi- 

 crinus, Apiocrinus roissyayius, and Uintacrinus we take to be 



