ON SOME PELMATOZOA FROM CHAZY LIMESTONE OF NEW YORK III 



the evidence seems to favor the idea that these brachioles 

 swung out as one continuous sheet and that the outer edge of 

 this sheet was subsequently broken away. This feature reminds 

 one of the arm of Cleiocrinus, a species of which I have found 

 in the same bed with Blastoidocrinus, and is another good 

 example of homoplasy. How much of the base of this sheet 

 could leave the internal plates of an ambulacrum is another 

 question. It seems to have been fixed at least up so far as 

 the eighth row of back plates. 



There remain for description some brachioles apparently 

 four in number, attached not to the deltoid but to the upper 

 ends of each pair of bibrachials. These appear to be biserial, 

 and are so at least in part, but they are small and tapering 

 and the arrangement of these plates is made out with exceeding 

 difficulty. The inner two are still more tapering and rudi- 

 mentary in character. They also possess no perfected hydro- 

 spires for the bibrachials are destitute of any such structure. 

 Are these old brachioles remaining attached to a plate that once 

 possessed a hydrospire system or are they new brachioles in the 

 building? If old, then the new brachioles must be formed 

 between the more mature outer ones and the last brachiole on 

 the deltoid; if new, they must be constantly pushed to the side 

 by still newer additions and one by one take their places on the 

 deltoid. There is no evidence to show brachiole formation 

 between these and the deltoid but these grade very regularl}'- 

 into the more mature forms and there are a number of brachioles 

 with their basal single plates still half on the bibrachial and 

 half on the deltoid. The fact, already mentioned, that these 

 lowest plates make practically no increase in size after being 

 given a position on the deltoid, is of itself significant in this 

 connection. 



Adambulacrals. Between the deltoids the coelomic cavity is 

 completely roofed over by an arched wall, concave inwardly, 

 consisting of a double row of alternating ( ?) adambulacrals. 

 Xhese plates, seen from the side, are somewhat in the form of 

 a parallelogram with the longitudinal axis about twice as long 

 as the transverse axis. The two long sides are slightly but very 

 regularly convex toward each other; each of the two ends 

 bears four obtuse angles. The middle face of the outer end 

 rests against the inner edge of a deltoid ; the face below this 

 sinks into the coelomic cavity and is parallel to the short side 

 of the brachial end of a hydrospire ; the outer face of the same 



