222 



The Ohio Naturalist. 



[Vol. XIV, No. 3, 



There are 39 ambulacral plates on one half-arm and 29 on the 

 other. The adambulacral plates, sometimes called the inter- 

 ambulacrals, alternate with the ambulacral plates. There are 

 forty of these on the one arm and twenty-seven on the other. The 

 skeleton is complete along the whole of the inter-ray in which the 

 madreporite lies except for the rows of the movable spines which 

 were based on the adanibulacral plates. 



Ca.Y in 



ai 



^^v- 





disc 



m 



,Tn«xclr£ Jporite 



a-mfciAJacrai /oUie. 



Fig. 1. Promo-palaeaster dyeri Meek (?). 

 part of disc and arms. 



Natural size, dorsal view 



There are a nmiiber of starfishes described in the publications of 

 the Ohio Geological Survey. Of these Palaeaster dyeri Meek, 

 (Plate 4 Vol. 1 part 2 of the Palaeontology) resembles most closely 

 the starfish under discussion. The specimen there figured was 

 of a larger animal than this one but as Professor Meek says in his 

 introductory statement, the poor preservation of the parts leaves 

 much to be desired in the description. 



The madreporite of P. dyeri is trilobate. Its shortest dimen- 

 sion is in the inter-ray and its longest at right angles to this in the 

 horizontal plane. These dimensions arc (> m. m. vertically and. 

 9 m. m. horizontally. 



The madrcporic body of my s])ccimcn shows a trace of this 

 lobation only. The vertical j^lane dimension is 7 m. m. while the 

 horizontal diameter is (i m. m. It has quite a different general 

 shape then from the madreporite of P. dyeri but the size is almost 

 the same relatively, in view of the sizes of the animals. The 

 appearance of the canals on the surface of the two madrcporic 

 bodies is very similar, though the pattern of the lines differs with 

 the shape of the bodies. 



