68 



l'ANAMIC DEEP SEA ECHINI. 



The largest specimen collected, 30 mm. in diameter, was somewhat 

 crushed. The apical system measured 19 mm. in diameter, the anal 14, 

 the actinal 10 mm. In this large specimen the buccal actinal plates were 

 somewhat irregular in shape, much as in the actinal system of a large 

 specimen of D. globulosum (PI. 26, fig. ..'). in younger specimens (PI. 25) 

 they arc marked for their great regularity of size. In a specimen 20 mm. 

 (PI. 26, fig. J) they show a tendency to irregularity, and one of the plates 

 is split into two near the distal side. Then' are in this specimen eight and 

 nine primary tubercles, with five ambulacral plates to each large interam- 

 bulacral plate. The milled ring of the primary radioles often spreads at 

 the base of the spines to a breadth of twice the diameter of the shaft 

 (PI. 25, fig. 5). 



19 mm 



Fig. 108. 

 Fk;s. 1D7-109. Dermatodiadema horril>um. 



In younger stages (PI. 27, fig. 2) the genital plates are uniform in size, 

 and remain so in older stages, with the exception of the madreporic genital, 

 which early develops into a larger plate (Pis. 27, fig. 8; 28, figs. 1, 3, .',), the 

 right anterior interambulacrum thus being wider than the others. 



