1888.] NATURAL SCIENCES OF PHILADELPHIA. 339 



rait plates, in conformity with these ideas, was discussed in the Ke- 

 vision of the Palreocriuoidea, Part. Ill, pages 44 to 59, and after- 

 ward in greater detail in our paper on the Summit Plates, above 

 referred to. 



Another consideration which strongly influenced us in adopting 

 this view was the supposed presence of a central plate in Haplocri- 

 mis, to which considerable importance was attached both by Car- 

 penter and ourselves in our discussions of the oral question, though 

 leading us to very different conclusions. On page 56, Kevision, 

 III, we said : "A far less objectionable interpretation of the central 

 plate than that given by Carpenter would be to regard it as a pos- 

 terior oral. In this case the orals would be represented by five 

 plates, and not by six ; the anus would be placed outside the oral 

 ring, and the radial dome plates would occupy the same position to- 

 ward the orals as the calyx radials toward the basals. But it would 

 place the mouth underneath the posterior oral, and it offers no ex- 

 planation of the central piece in Haplocrinus" 



This theory seemed to us at that time very plausible, and we 

 should have advocated it, if it had not been for the central plate 

 in Hafplocrinas, which we discovered, as we supposed, in a speci- 

 men of H. niespiliformis, our observation being verified by Carpenter, 

 to whom we sent the specimen for examination, (Challenger Report, 

 page 158). 



When we took up a year ago, the investigation of the Larvi- 

 formia, the group to which Haplocrinus belongs, we had before us 

 the original specimens of H. \'lio from New York, and found 

 ourselves unable to discover any suture between the so-called central 

 plate, and the posterior vault plate, and we began to suspect there 

 was something wrong about the central plate. During a visit of one 

 of the writers to Europe in the winter of 1887-8, he procured in the 

 Eifel mountains a very large series of good specimens of H. mes- 

 piliformis, with a view to ascertaining if possible the real fact about 

 the central plate, and also the anal opening which was fully as great 

 a mystery. These specimens at once disclosed the fact that the 

 "central plate" is a myth, and that what had before been taken for 

 it was simply a more or less tongue-like or polygonal prolongation 

 of the posterior plate, sometimes surmounted by a small node — the 

 "knopf" of Goldfuss. We had mistaken a fracture in our original 

 specimen for a suture on the posterior side, and have seen another 

 in which a similar mistake might have been made if one had that 



