70 



PANAMIC DEEP SEA ECHINI. 



new plates. The same larger anal plates exist in a somewhat older speci- 

 men (PI. 27, fig. 4) of 12 mm., Fig. 112, with an outer circle of ten 

 secondary plates arranged in pairs. 



In the next stage of 1-4 mm. the eight anal plates, Figs. 113, 114, still 



H HOREIDUM. 



persist, as they do to 30 mm. in diameter, hut they are more or less disturbed 

 in their arrangement, and we find (PI. 27, figs. 5, 6) an outer circle of seven 

 and nine pairs of plates. In a specimen of 20 mm. in diameter, Fig. 115, 

 there are twenty-five pairs of outer secondary anal plates (PI. 28, fig. /), 

 and in another specimen of the same size, Fig. 116, there are no less than 

 forty-six pairs of secondary anal plates (PI. 28, fig. .'). 



fUL, 



D. HORRIDUM. 



In Dermatodiadema, where the ambulacral plates play but an insignifi- 

 cant part in supplying the actinal system with calcareous plates some of 

 the first actinal plates remain in contact with the actinal system in quite 



