1885.] NATURAL SCIENCES OF PHILADELPHIA. 245 



arc abactinal plates, that they constitute; a part of the calyx ; and 

 it proves further, which is equally important, that some of the 

 Palaeocrinidse have abactinal [dates along their ventral side. That 

 C. alutaceus cannot be retained in the same genus with the Car- 

 boniferous forms is self-evident. The two are morphologically 

 in a very different condition, and we should propose for the former 

 a new generic name if we had before us specimens in place of 

 figures. 



Carpenter fully accepts the views previously held by us, that 

 in the Camarata all interradials located dorsally are abactinal 

 plates, and those at the ventral side actinal. It should be stated, 

 however, that we had communicated to him, in time for the Chal- 

 lenger Report, the modifications our views had undergone on this 

 point. We make this statement to show that Carpenter's inter- 

 pretation of the plates was not based upon our — as we believe — 

 erroneous observations, but was the result of his own studies. 

 Carpenter even goes further than we ever did. He asserts that 

 the plates, which we took to be the actinal representatives of the 

 interradials, in some groups, are anambulacral plates, and form 

 a part of the disk. 



His interpretations of the interradials in the Platj'crinidae are 

 not always harmonious. If we understand him correctby, he 

 regards the first interradial piece as a calyx plate (Chall. Rep., p. 

 40 ), but all succeeding ones as perisomic, " much more substantial, 

 however, than in Neocrinoids, and forming part of the solid 

 covering, but not a true vault or tegmen caHcis" (Chall. Rep., p. 

 179). On the same page he states further: " Although believing 

 that the vault of a Platycrinoid corresponds collectively to the 

 orals, interradials, ambulacral and anambulacral plates of Neo- 

 crinoids, I do not wish to assert that the Plat3^crinida3 either had 

 an external mouth or open ambulacra on the disk." On page 1T8, 

 however, he states that the " series of four or six interradials, 

 corresponds generally to the single large interradial of Cyatho- 

 crinus" It is not clear to us, how the same pieces can be anam- 

 bulacral, i. e. disk plates, and at the same time "correspond 

 generally " to a true interradial plate. He supports his theory 

 by pointing to the alternating pieces, the so-called "covering 

 plates," which in most of the Platycrinidse appear along the radial 

 portions of the ventral surface, and which he believes are always 

 subtegminal in Actinocrinus. He says : " I do not myself think 



