JAPANESE ASTEEOIDEA. 



189 



is the presence of a small spine on the superomarginals ; but, as 

 will be shown later on, this is subject to considerable variation, 

 and these spines may even be entirely absent in some specimens. 

 Radial ratio. — The radial ratio has a larger range of varia- 

 tion than might be inferred from the previous descriptions. We 

 again see that, as a general rule, it is less for specimens with 

 smaller radii. The measurements are tabulated below. 



