Plate 39. 



1-2. Colobocentrotus Mertensii Brandt. 



1. Showing the right posterior ambulacrum, with the right posterior interambulacrum, 



and a part of the right anterior ambulacrum. * 



2. Showing the odd posterior interambulacrum with the bivium, and half of the right 



posterior ambulacrum. 



3-4. Colobocentrotus Stimpsonl A. Ag. 



3. The right posterior interambulacrum, with the right posterior ambulacrum and a part 



of the right anterior ambulacrum. 



4. The right anterior interambulacrum, with the right anterior ambulacrum and a part of 



the odd anterior ambulacrum. 



1-2 are from a specimen of 70 mm. in diameter, and 3-4 from a specimen measuring 

 88 mm. in diameter, including the spines. The dotted lines join the radioles of the same 

 vertical row. 



Boniu Ids., N. P. Ex. Ex., Dr. Wm. Stimpson Coll. 



