154 



PAN AMI C DEEP SEA ECHINI. 



The ambulacra! areas are bare where the phyllodes are developed, about 

 half-way from the actinostome to the ambitus (Pis. 72, fig. 1 ; 73, fig. 1) ; 



beyond that point they are covered 

 with small secondaries as in the in- 

 terambulacral plates (PI. 72, fig. i). 

 Round tin- anal s\stem (PI. 73, fig. ■',) 

 the tuberculatum is coarse likethatof 

 the interambiilacral plastron. The 

 anal system is partly on the actinal 

 side and partly on the ambitus. It 

 is longitudinally slightly elliptical 

 (PI. 73, tig. -'), covered with concen- 

 tric rows of trapezoidal plates; the 

 outer row is composed of larger 

 plates, they all carry small tubercles. 

 The anal opening is subcentral to- 

 wards the actinal edge. 

 The sternum of U. giganteus is polygonal, narrower towards the actino- 

 stome, Fig. 221, and proportionally much larger than the elongate heptago- 



nal sternum of U. Naresianns, 1 Fig. 223, 

 which is followed by large episternal plates, 

 Fig. 222. 



Fig. 221. Ukeluinus giganteus. 



b S a 



Fig. 222. Urechints Naresiani • 



After Loven. 



13 mm. 



Fig. 223. U. Nam -i \\i - 



The actinostome is circular, depressed (Pis. 72, fig. / : 73. fig. /). covered 

 with an outer row of large triangular plates with smaller elongated plates 

 between these and the actinal opening. In this large specimen the rudi- 



1 In Calymne the plastron is like that in Urechinus, the labium is small, followed by a single 

 plate and then by the double plates. This corresponds to the first ami second interambulacral plat's 

 lit Cystechinus. 



