Mr. F. A. Bather on British Fossil Crinoids. 327 



The first point of Messrs. Wachsmuth and Springer, that 

 the Azygos plate is a primitive element of the dorsal cup, 

 rests on two assumptions. First, that Baerocrinus has only- 

 four radials and that the fifth plate is the azygos plate. In 

 any case Baerocrinus is an abnormal form, but I fail to see 

 that it becomes any more normal by this explanation. As 

 there are two plates in the dorsal cup, neither arm-bearing, 

 but each like the other and both in all other respects like the 

 three radials, there is no conceivable reason why one should 

 be called a Radial and the other an Azygos plate ; except 

 indeed the reason that Messrs. Wachsmuth and Springer's 

 hypothesis would not otherwise hold water. The second 

 assumption is that the lower halves of certain radials are 

 embryonic plates. The dorsal cup of the early Pelmatozoa 

 may no doubt have contained more plates than the fixed 

 number of the Fistulata : but these plates, if any of them re- 

 mained, would, as in Acrocrinus, alternate with the rest, and 

 would probably be below the basals. On the other hand the 

 compound radials of Heterocrinus and similar forms simply 

 resemble an ordinary radial horizontally bisected, and as such 

 they have been regarded by all other authors. Possibly the 

 object of this structure was to give greater flexibility to a cup 

 in which the more movable forms of joint were as yet un- 

 developed. At any rate, since the azygos plate is admitted 

 to be the homologue of these lower segments of the radials 

 there can be no adequate reason for regarding it as a primitive 

 element of the dorsal cup. 



Let us now consider the second point, viz., the derivation 

 of the anal x and right posterior radial from the azygos 

 plate Az. In the first place I fail to understand what Messrs. 

 Wachsmuth and Springer mean by one plate absorbing 

 another. A plate may be absorbed by the general tissues of 

 the body in the individual, or it may be developed to a less 

 extent in a line of descendants ; at the same time other plates 

 may increase in size and may ultimately occupy the room of 

 the former : but to say that these plates absorb the other is 

 either an incorrect or an unscientific statement. The deriva- 

 tion of the right posterior radial from Az cannot therefore be 

 by any process of absorption ; although it might, as P. H. 

 Carpenter has suggested, make its first appearance as a small 

 arm-bearing portion cut off from Az. But why should this 

 be the origin of the right posterior radial alone? Why 

 should not the upper radials of Heterocrinus, Ectenocrinus, 

 and AnomaJocrinus be similarly derived from the lower 

 radials ? This then is not only an assumption, but an incon- 

 sistent one. Similarly the derivation of x from Az is an 



