PANAMIC DEEP SEA EOHTM. 



terior one. The relative proportions of the actinal system and of the test 

 do not vary materially in the different stages of growth, Fig. 121. 



Although the ambulacral plates of the Aspidodiadematidse are small and 

 of nearly uniform size (Pis. 25, figs. 1,3; 26, figs. 1, 4), much as in the 

 Cidaridse, yet in older specimens the actinal plates become slightly petaloid 



ra 



.a 



10 mm 15 mm. 



FIG. 123. Fio. 124. 



Figs. 122-125. D. horridum. 



20 mm. 



Fig. 125. 



crowded and pushed inward (PI. 26, fig. #), as in the Echinidae, and the 

 actinal plates pass from simple plates extending across the ambulacrum, 

 Fig. 122, to small intercalated plates reaching but little beyond the median 

 line of each ambulacral zone, Fig. 91. In the younger stages. Fig. 122, 

 the ambulacral plates are symmetrical at the actinostome ; with increasing 

 age, they become more and more asymmetrical, Figs. 123, 124, 125, as 

 the gill cuts become more prominent. 



In both the species of Dermatodiadema here described the plates of the 

 genital ring are of equal size in young stages (Figs. 99, 100) ; with increas- 

 ing age the madreporic plate becomes longer, Figs. 126, 127. This is 



D. GLOBULOSUM. 



already seen in a specimen of 20 mm. in diameter, Fig. 96. In D. glolulosum 

 the anterior ocular plate sometimes increases in length but not in width 

 with the growth of the madreporic plate, Fig. 126. In D. korridum the odd 

 ocular shows gradual increase in length in young stages of 10.5 mm. in 

 diameter, Fig. 100, and the increase in size of this plate keeps pace with 

 that of the madreporic plate, Fig. 96, while in D. glohdomm the madreporic 

 plate sometimes increases alone in width and length beyond the other 



