154 



PANAMIC DEEP SEA ECHINI. 



The ambulacral areas are bare where the phyllodes are developed, about 

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



beyond that point they are covered 

 with small secondaries as in the in- 

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

 Round the anal system (PI. 73, fig. .;) 

 the tuberculation is coarse lil^e that of 

 the interambulacral plastron. The 

 anal system is partly on the actinal 

 side and partly on the ambitus. It 

 is longitudinally slightly elliptical 

 (PL 73, fig. 5), 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. giganteiis is polygonal, narrower towards the actino- 

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



nal sternum of U. Naresianus,^ Fig. 223, 

 which is followed by large episternal plates, 

 2 I Fig. 222. 



Fig. 221. Ubecuixus giganteus. 



b 5 a 



Fio. 222. Ukkchints Naresianus. 



AlTBB Lovte. 



Kt una. 



Fig. 22;J. U. Naresiants. 



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- 



^ Tn Calymne the pla.stron ia like tliat in I'reclnnus, the labium is small, followed by a single 

 plate and then by the double plates. This corre^{x>nd3 to the first and second interambulacral plates 

 of Cystechiiius. 



