Plate 43. 

 1-7. Colobocentrotus Stimpsoni A. Ag. 



1. The abactinal system, before being denuded of its spines. 



2. The abactinal system of the same, denuded. 



3. The same, seen from the interior of the test. 



4. The auricles of the right posterior ambulacrum, seen from the interior of the test. 



5. The auricles as seen looking towards the actinostome through the auricular opening of 



the left posterior ambulacrum. 



6. Plates of the right anterior interambulacrum adjoining the actiual system, seen from 



the interior of the test. 



7. Plates of the odd posterior interambulacrum bordering on the actinal system. 

 Figs. 6, 7, seem to show the remnant of the arabulacral primordial plates. 

 From a specimen measuring 88 mm. in diameter including the spines. 



Benin Ids., Captains Einggold and Rodgers, N. P. Ex. Ex., Dr. Wm. Stimpson Coll. 



