94 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



be noted in figure 3. Here the infrabasals are greatly diminished 

 in size, while there is a corresponding increase in the size of the 

 centrale. Here there seems to be no possibihty of a fusion between 

 the members of the infrabasal circlet. In case fusion had taken 

 place subsequent to this stage the infrabasals would have united 

 directly with the centrale. In figure 5 there was a similar reduction 

 in the size of the infrabasals before, or, perhaps, during, the process 

 of fusion. The tendency was toward the elimination of the infra- 

 basals as distinct elements, and whether the result was obtained by 

 the simple fusion of the plates concerned, irrespective of the order 

 in which such fusion took place, or by the partial resorption of the 

 infrabasals and their subsequent coalescence with the centrale, was 

 of little moment. 



Springer styles all those apical plates that meet interbasal sutures 

 by more than one angle, ''centrales." Thus in figure 8 we find two 

 "centrales," and in figure 7 two centrales and one infrabasal. Such 

 types he describes as having a double centrale. As previously stated, 

 Springer does not attempt to explain how two centrales could by any 

 chance have been produced in an individual. He merely states that 

 "all these irregular cases are rare and exceptional, and constitute 

 mere individual variations." Two such plates could certainly not 

 represent a "proximal or distal stem ossicle." If a gap existed to be 

 filled, one plate would have been formed — not two. The only other 

 possible explanation for a "double centrale" is that one of these 

 plates is composed entirely of fused infrabasals, and the other made 

 up of the primitive centrale to which one or more infrabasals have 

 fused. 



Springer calls attention to the fact that in the case of figure 6 the 

 centrale is both interradial and radial. Hence it follows according 

 to the law of Wachsmuth and Springer, which "strictly prevails," 

 that this individual is at one and the same time monocyclic and dicy- 

 chc. This is obviously impossible. The specimen does, however, 

 combine features typical of forms M and D as shown by Uintacrinus. 

 This same plate beautifully illustrates my contention that the shape 

 of the centrale is entirely dependent upon the plates surrounding it. 

 On one side the centrale rests against three infrabasals, and conforms 

 to the angles between these plates. As a result, on that side it is 

 interradial. On the other side it has fused with the other two infra- 

 basals, and after a process of mutual adjustment between itself and 

 the basals, one complete and two incomplete sides of the pentagon to 

 be have been formed, the inclosed angles conform to the basals and 

 are radial in position. 



Inasmuch as Form M in Uintacrinus is not truly monocyclic, we 

 may well pass over the last objection of Springer on pages 33 to 34 

 in regard to the supposed change in orientation of the chambered 



