73 



lateral arms. The arms are of medium length, narrow, with a more or less 

 distinct widening at the point. There is a not very conspicuous cluster 

 of red pigment cells in the point of the arms; series of pigment cells are 

 also seen along the vibratile band in the lobes, in the postero-lateral pro- 

 cesses and along the postoral and preoral band. In the body and arms 



N 



Fig. 26. Larva of Echinometra lucunter, 15 days old; ventral view. "^"/i. a. anal opening; 

 al. anterolateral arm; am. amnion; da. dorsal arch; oe. mouth; pb. posterior ciliated band; 

 pd. posterodorsal arm; pi. posterolateral process; po. postoral arm; ,pr. preoral arm; prb. 

 preoral ciliated band; ptr. posterior transverse rod; vl. vibratile lobe; vtr. ventral trans- 

 verse rod. 



some irregularly scattered pigment cells are also found. The stomach is 

 yellow. 



In the skeleton the most noteworthy feature is the structure of the 

 posterior transverse rod, which ends in the two usual branches, the lower 

 of which is the longer and set with a series of 4 — 5 thorns along its lower 

 edge (Fig. 27). The postero-dorsal rod is fenestrated, distinctly curved 

 in the basal part. The dorsal arch has a rather long, simple median process 



10 



