1888.] NATURAL SCIENCES OF PHILADELPHIA. 343 



ambulacra pass out to the rays. The first of these objections, which 

 was raised by us already in Revision III, p. 56, is readily explained 

 if we suppose that the posterior oral was pushed inward over the 

 mouth by the plates connected with the anus, and that this became 

 a constant character in palaeontological time. The presence of a 

 single large central plate in Talarocrvius, etc, may be accounted for 

 by resorption of the four anterior orals, the posterior plate actually 

 performing the functions of all. It might also be possible that this 

 large plate in these forms represents the whole oral pyramid, five 

 plates coalesced, in a similar manner as the basals in some instances 

 at the dorsal side. 



These considerations were quite sufficient to convince us that the 

 five orals of Neocrinoids were represented in the Palaeocrinoids by 

 both the central plate and four large proximals taken together ; 

 thus in a large measure reconciling the conflicting views of Carpen- 

 ter and ourselves upon this question — the orals being found at last 

 to consist of a portion of the proximals which he has claimed, with 

 the addition of the central plate which we have contended for. 

 This rational result, as often happens in such cases, adopts Avhatw^as 

 sound, and rejects the errors in the views of both parties. 



The evidence which we had obtained was entirely satisfactory to 

 ns, and we were prepared upon the foregoing facts to announce our 

 final conclusion, as above stated, when we made a most unexpected 

 discovery, which in oar judgment not only settles the oral question 

 in conformity with these views beyond all controversy, but bears so 

 strongly upon questions of classification, that it may justly be regard- 

 ed as one of the most important discoveries ever made in palaeozoic 

 crinoids. 



In the Ichthyocrinidae the ventral structure has been hitherto 

 almost totally unknown. Some small plates had been seen on the ven- 

 tral side in a few instances, apparently belonging to a plated integ- 

 ument, but not in a condition to afford much information, and its 

 real nature has been a matter of conjecture and theory. We have 

 been of the opinion that it was a vault, covering a subtegminal 

 mouth and ambulacra, but pliant, yielding to motion in the calyx 

 and arms; while Carpenter believed that it Avas a disk paved by 

 plates as in some of the Neocrinoidea. It was evidently of the most 

 fragile construction, and this, together with the fact that in this 

 family the arms are generally found closely folded and firmly im- 

 pacted over the vault, was strongly against the probability of ever 



