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



are shown distinctly in many of the specimens and are not 

 accidental. They would serve as passages for podia or other 

 tubes of an ambulacral system. 



The bases of the covering plates in a specimen of A. pileiis 

 is shown in Figure 7, Plate I. This indicates also the very 

 small size of the food groove (in front of the black arrow) 

 which ran beneath the cover plates and above the row of 

 flooring plates. 



Rate of Growth. 



If size can ever be considered a specific character the forms 

 under consideration range from A. holbrooki, over 30 mm. in 

 diameter, A. cincinnatiensis, 27 mm., A. pileiis, 20 mm., A. 

 rectiradiatus, 17 mm., A. austini var. lawshe, 17 mm. to A. 

 austini from Dutch Creek, 10 mm. The numbers of pairs of 

 cover plates in the ambulacral ray corresponds roughly with 

 the diameter of the specimen. 



Where the plates at the beginning of the ray were indistinct 

 the number is preceded by an x, where indistinct at the distal 

 end the number is followed by y. Only the outer row of cover 

 plates was counted in any case. 



TABLE. 



These arms which were notably deficient or indistinct were 

 omitted entirely from the count; those unnamed being austini 

 or related forms. 



