1890.] NATURAL SCIENCES OF PPIILADELPHIA. 349 



surface of the internal casts, and represents tlie ambulacral plates 

 developed in the perisonie of recent Crinoids." He also admits " the 

 complete resemblance between the ventral perisome of a recent Cri- 

 noid and the upper surface of the body beneath the vault of an 

 Adinocrinus." Vault and ventral disk, he says, " are entirely dis- 

 tinct structures." Of the vault, he says further (p. 172) " I be- 

 lieve the oral or actinal system forming the vault of Actinocrinns to 

 have been developed on the left larval antimer, in exactly the same 

 way as the apical or abactinal system is developed on the right ; but 

 the oral system, insteadof being limited to five oral plates as in Neo- 

 criuoids, Beached a very extensive development, so that in its coni- 

 pletest form it represents such a parallel to the apical or abactinal 

 system as is to be met with in no other Crinoid." From these passages 

 and others in the Challenger Report, especially on p. 180,' to which 

 we shall refer again, it appears Dr. Carpenter supposed that in Act- 

 iuocriuns all plates of the calyx up to the arm bases were abactinal, 

 and all constituting the ventral side actinal, not only the orals and 

 the so-called radial dome plates, but also the smaller plates, the so- 

 called interradial dome plates, surrounding them. Similar views 

 were held by us and advocated in Pt. II of the Revision (pp. 14 to 

 21), but abandoned in Pt. Ill, (pp. 16 to 27) as to the interradial 

 dome plates, which we regarded as a continuation of the interradial 

 plates of the dorsal cup, and not as actinal structures. 



All interradial and interaxillaries, not only in the Camerata but 

 wherever they exist in recent or fossil Crinoids, increase by multi- 

 plication in the growing animal, and as such, are auxiliary pieces 

 filling up spaces between the rays and their sub-divisions. They 

 increase primarily in an upw'ard direction, but partly also by inter- 

 calation, secondary plates being introduced between the primary 

 ones. It is owing to the intercalation of these supplementary pieces 

 that the arrangement of the interradial plates in the upper rows is 

 less regular than it might be otherwise. In the simpler forms such 

 supplementary pieces are wanting, or they occur only around the 

 arm bases ; while in the Reteocrinidae they constitute the greater 

 part of the interradial and interaxillary areas. In this family 

 small pieces in large numbers continually formed in the growing 

 Crinoid along the margins of the radials and brachials, and between 



1 All quotations from the writings of Dr. Carpenter, if not otherwise stated, 

 are from the Challenger Report on the Stalked Crinoids. 



