290 PROCEEDINGS OF THE ACADEMY OF [1885. 



flexible calyx, with a flexible vault, may not enclose a soft or 

 even a plated disk such as we find in Crotalocrinus and Enallo- 

 crinus. The thiuness and irregularity of the plates is no valid 

 argument against it. We find such plates ventrally in Glypto- 

 crinus and some species of Physetocrinus, and there are plates 

 of the same nature dorsally in the Reteocrinidae. On the other 

 hand we find massive and more or less regular plates dorsally in 

 Apiocrinus, which Carpenter considers to be perisomic. To our 

 minds the case of Extracrinus is by no means parallel to that of 

 the Ichthyocrinidae, as that genus is destitute of calyx inter- 

 radials. If his argument were correct, then all the plates of the 

 Ichthyocrinidae and Reteocrinidae should be considered as peri- 

 somic. In that case the perisomic portions of the Crinoid would 

 predominate so enormously that nothing would be left for the 

 abactinal part except the base, and species of Beteocrinus, which 

 so good an observer as S. A. Miller considered as congeneric 

 with Glyptocriiius, would constitute a distinct order. And we 

 would have the anomaly that the earliest known forms of Crinoids 

 would be in this respect examples of the highest organized types, 

 and most closety allied to the recent Crinoids. 



In support of his view, Carpenter has no other proof than this 

 superficial resemblance. There is no evidence of the existence 

 of external food grooves, which must follow if these plates are 

 perisomic. The same reasons that led us to regard the smaller 

 interradials in Apiocrinus — massive as they are — as perisomic 

 plates, compel us to consider all plates of the Ichthyocrinidae, 

 interradial in position, as belonging to the same element, and 

 either all perisomic or all calyx plates. 



If the plates in question were perisomic, it would obliterate the 

 last distinguishing feature between Neocrinoidsand Palaeocrinoids, 

 and we should like to know upon what points Carpenter would 

 separate the Ichthyocrinidae and Reteocrinidae from the Neocri- 

 noidae. We admit that the direct proof of our views as to the 

 ventral structure of the Ichthyocrinidae is as yet wanting, but in 

 this respect Carpenter is no better off, and it seems to us that the 

 weight of argument from analogy is in our favor. 



The Relations of the Pal^eocrinoidea to the Neocrinoidea. 



The name " Palaeocrinoidea " was proposed by one of us in 1877 

 (Amer. Journ. Sci., vol. xiv, p. 190), but not properly defined 



