328 Mr. F. A. Bather on British Fossil Crinoids. 



assumption, and one that does not harmonize with the facts ; 

 for the two plates are widely separated in such early forms 

 as Ectenocrinus, Atiomalocrinus, and probably in Heterocrinus , 

 Iocrinus, and Merocrinus. It may indeed have been this 

 obvious objection that made Wachsmuth and Springer main- 

 tain that the axillary plate of Iocrinus consisted of R and x 

 fused. This supposition, however, for which no other reason 

 can be found, would lead to an inconsistency of a different 

 kind. In no other genus of the Fistulata does the plate x 

 support the ensuing plate (t) of the ventral tube on its left 

 side : this fact was well known to Messrs. Wachsmuth and 

 Springer in 1879, but they seem to have overlooked it in 

 1886. 



Finally, the earlier stages of the evolution as set forth by 

 Messrs. Wachsmuth and Springer entirely depend on the 

 foregoing assumptions, to which such exception can be taken. 

 And not only this, but they derive Dicyclica from Mono- 

 cyclica and these again from Pseudomonocyclica. And again, 

 starting from forms without pinnules, they pass through 

 forms with pinnules back to forms without pinnules, and then 

 to forms with pinnules again : this would have been all very 

 well in 1879, but is totally inconsistent with the importance 

 they attach to pinnules in 1886, when separating the Cyatho- 

 crinida? from the Poteriocrinidge. 



What then are the true homologies and relations of the 

 plates of the anal area ? The so-called " azygos " plate 

 I follow P. H. Carpenter in regarding as primitively the 

 lower portion of the right posterior radial. Really there is 

 little choice in the matter. Everyone is agreed as to which 

 plate is the azygos in the various genera, and it is always 

 found adjoining the right posterior radial. In the majority 

 of the earlier forms it occupies a position immediately below 

 the radial, e. g. Iocrinus (5), Heterocrinus (6), Ectenocrinus 

 (7), Anomalocrinus (8), Merocrinus (11), Dendrocrinus (15), 

 and in three of them it is exactly paralleled by other radial 

 segments. It is hard to imagine that it began at one side of 

 the radial in a few confessedly abnormal forms, that it sud- 

 denly found its way to a situation beneath the radial, and 

 that it slowly worked its way back to its former position. 

 Holding then the view that this plate is morphologically a 

 radial element, I regret that the name " azygos " should ever 

 have been applied to it. Words, we know, have a powerful, 

 though often unconscious, influence on thought, and it occurs 

 to me that the selection of this word by Dr. Carpenter led 

 Messrs. Wachsmuth and Springer to their idea that it was 

 a primitive independent element of the dorsal cup. Dr. Car- 



