72 The Ohio Journal of Science [Vol. XIX, No. 1, 



Agelacrinite from the Elkhorn, Figures 25 and 25A, the five 

 rays are rather close in their origins and the aboral extensions 

 of any plates to stiffen the peristomial ring would be less neces- 

 sary. There may be sometimes a small plate in place between 

 rays 2 and 3 and rays 3 and 4, but it is not sufficiently elongate 

 aborally to call attention to itself, in most cases. Nor does it 

 seem as though in the specimens at hand the R. and L. peris- 

 tomial plates were far enough apart to be represented from the 

 aboral side as these stiffening plates. I should prefer to consider 

 these two intervening plates when present either as descendants 

 of cover plates between the pairs of rays and anterior ray or 

 possibly they might be the first inter-radial plates of the inter- 

 radial areas in which they lie. 



It has been shown that the posterior peristomial plate 

 is made by the fusion of plates, the middle one of which might 

 be considered as the apex of the anal inter-radial space. The 

 anterior peristomial plates likewise must be made up of a 

 fusion of cover plates, but I have no evidence that there are 

 inter-radial plates involved. Hall calls these plates V shaped 

 and if they are made of cover plates from ray 3 and of cover 

 plates from between rays 2 and 4 the V shape would be the 

 natural shape. Most that I have seen, however, are quad- 

 rangular and so there is the possibility of the incorporation of 

 the first inter-radial plates from the respective areas. 



FLOORING PLATES. 



After the first flooring plates of each ray which surround the 

 substomial chamber with the help of the posterior peristomial 

 plate, the ray as seen from the aboral side is continued as a 

 series of quadrangular plates, upon which the covering plates 

 already seen from the oral side stand. These floor-plates join 

 each other by a slightly beveled joint, the proximal end of each 

 plate sliding slightly over the distal end of the next plate inward 

 toward the mouth. This joint has the greatest slant or bevel 

 in A. cincinnatiensis and the least, almost a vertical joint, in 

 A. austini var. lawshe. 



There is another beveling of these plates on the lateral 

 (oral) surfaces in A. cincinnatiensis. On these lateral slanting 

 surfaces stand the outer row of cover plates. I do not find this 

 articular surface on those forms which have less nearly two 

 pairs of rows of cover plates for each ray. 



