Plate 42. 



1-8. Colobocentrotua Stimpaoni A. Ag. 



1. Interior view of the actinal side. 



2. One of the pairs of perforated plates of the buccal membrane, facing the odd anterior 



ambulacrum. 



3. Exterior view of the odd anterior ambulacral plates adjoining the actinal system. 



4. The same seen from the interior of the test. 



5. The tenth plate from the actinal system of the odd anterior ambulacrum. 



6. The same seen from the interior. 



7. Interior view of a plate of the right posterior ambulacrum at the ambitus. 



8. The ocular plate and the abactinal extremity of the left posterior ambulacrum, seen 



from the interior. 

 In figures 3, 4, and 5, 6, a small cross shows the slanting perforation of the pore through 



the test. 

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

 Boniu Ids., Captains Riuggold and Rodgers, N. P. Ex. Ex., Dr. Wm. Stimpson Coll. 



