1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



351 



We have found this rule to be without exception among palseozoic 

 crinoids, and upon the strength of this, and an examination of the 

 column of such Neocrinoids accessible to us as possessed an angular 

 column, or cirri, we came to the conclusion, as stated in the Revision 

 III, p. 8, that "probably many Neocrinoids either possess small 

 underbasals, or these were jDresent in their larval form. " We became 

 more and more of the opinion that the Neocrinoids, for the most part, 

 were built on the plan of dicyclic crinoids, and we again stated (Rev 

 III, p. 7 1 ), that "all Neocrinoidea, or at least the most of them, in their 

 larval state may have possessed rudimentary underbasals, hidden by 

 the column. " On pages 294-299, we discussed this question more 

 at length, and stated our conclusion to be (p. 298) that "either the 

 rules which meet with no exceptions among Palaeocrinoidea, as far 

 as we know, do, not hold good for the Neocrinoidea, or the genera to 

 which we alluded, and which are built otherwise upon the plan of 

 dicyclic crinoids, really possessed rudimentary underbasals during 

 life, as Extracrinus and certain species of Millericrinus, or that 

 perhaps underbasals were present in their larva. The ventral surface 



1 Our observations respecting the column were naturally restricted to species 

 in which the stem and axial canal are angular, and in alluding to the sections and. 

 sutures of the column we refer to species with a pentapartite stem. In cases in 

 which only basals are visible, and the angles of the stem are interradial, underba- 

 sals invariably are present beneath the column. 



