72 



PAXAilJC DEEP SEA ECHINI. 



pairs of interambulacral plates, with one plate of the seventh in each 

 interambulacral area (PI. 25, fig. 1). 



In a somewhat older specimen of 10.5 mm., Fig. 118, the first pairs of 

 interambulacral plates are but slightly reduced in size. There are sixteen 

 to seventeen pairs of ambulacral plates. The seventh pairs of interambu- 

 lacral plates are fully developed, with the eighth indicated in each inter- 

 ambulacrum (PI. 25, figs, .', 4 ; 29, figs. 1, ..'). 



In a specimen of 15 mm., Fig. 119, the first pairs of actinal interam- 

 bulacral plates have been resorbed in all the interambulacra except the left 

 posterior, the right anterior, and the odd interambulacral area, where one 

 plate is left, the second pairs of plates now being elsewhere in contact with 

 the actinal system. 



15 hum. 



Fig. 119. I), horridtjm. 



There are twenty and twenty-one ambulacral plates. The eighth pairs 

 of interambulacral plates are fully developed, and the ninth pairs are in- 

 dicated in all the ambulacra (PI. 25). 



In a specimen of 20 mm. (Pis. 26, fig. 1 ; 28, fig. 1; 29. figs. 3, /,), with 

 twenty-two to twenty-three ambulacral plates, Fig. 12U, the actinal inter- 



