222 PROCEEDINGS OF THE ACADEMY OP [1886. 



clic older Ciinoids. This departure from what we discovered to 

 be the rule in the Palteocrinoidea induced us not to mention the 

 axial canals in suggesting on p. 71 that perhaps " all Neocrinoids, 

 or at least many of them, may have possessed in their larval state 

 rudimentary underbasals hidden by the column," basing our argu- 

 ments mainly upon the interradial angles of the column and the 

 radial position of the columnar cirrhi. This forms at present an 

 objection to our view that the two genera, and especially Penta- 

 crinus, are dic^xlic. On the other hand it must not be over- 

 looked that the position of the column, whether radial or inter- 

 radial, apparently is governed by laws similar to those by which 

 the underbasals are radial, the basals interradial. The pentapar- 

 tite stem and this is found in quite a number of palaeozoic genera, 

 especially Silurian alternates always with the proximal ring of 

 plates, the segments are radial when there are basals only, inter- 

 radial when also underbasals are present. In Paheocrinoids in 

 which the column is undivided and pentangular, its position, 

 whether radial or interradial. is ascertained from its lateral angles, 

 and hence their direction morphologicallj^ important. In species 

 in which the underbasals are small, and completely covered by 

 the column, as sometimes in Barycrinus, the angles of the column 

 occupy the same relative position toward the basals, as the upper 

 stem joint of Metacrinus, Pentacrinus, Millericrinus and the cen- 

 trodorsal of all Comatulge does toward their basals. This led us 

 to the conclusion that either the rules, which meet with no excep- 

 tion among Palseocrinoidea, as far as we know, either 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 rudimentarj^ underbasals during life as Extracri- 

 nus and certain species of Millericrinus^ or that perhaps under- 

 basals were present in their larva. 



The ventral surface of the centrodorsal in some species of 

 Antedon is almost identical with that of the top stem joint of 

 Millericrinus,t\iQ plate is also interradial (PL 6, fig. 11), and 

 rests, as in the Apiocrinidse, against the outer face of the basals, 

 not within the basal ring. It is similar in other Comatulae, in all 

 of which the centrodorsal is interradial, and upon this mainly, we 

 base the opinion that perhaps also the Comatulae in their early 

 larva had rudimentary underbasals. That these plates, if present, 

 were not observed, is not surprising, as they may have been very 

 minute and been covered entirely b}' the column. 



