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ECHINODERMATA— ECHINOZOA 



PHYLUM IV 



petaloid ventrally, narrow dorsally, pore-pairs uniserial. Eleven to fourteen 

 columns of plates in an interambulacral area. Small primary and secondary 

 tubercles on interambulacral plates. This genus is highly specialised, 

 particularly as regards the interambulacra which attain the greatest number 

 of columns of plates and the most accelerated development of the same known 



A, Palaeechinus quadriserialis Wright. Lower Carboniferous ; Rathkeale, County Liinerick, Ireland, i/^. 

 B, Apical disk of same, 2/j. Restorations indicated by dotted lines. C, Same species, Middleton, County 

 Cork, Ireland. Ambulacral detail, enlarged (after Jackson). 



in Echini. H. rarispinus (Hall) is a greatly flattened species, H. pentagonus 

 Jackson is pentagonal in outline, and H. beecheri Jackson is ventrally 

 flattened and bilaterally symmetrical. Lower Carboniferous ; North America. 

 Fholidechinus Jackson. Test high, spheroidal, ambulacral areas narrow 

 throughout, pore-pairs moderately biserial. Nine to ten columns of plates in 

 an interambulacral area. Secondary spines and tubercles only. Lower 

 Carboniferous ; North America. 



