Bd. VI: 4) 



THE ECHINOIDEA. 



37 



ever, most of these are calculated in percent I give here some direct measurements, 

 finding that it may not infrequently be preferable to have the direct instead of the 

 percent numbers; further these measurements will be of importance for judging of 

 the value of the varieties of this species established by DÖDERLEIN. 



Concerning the tuberculation it may be remarked that the secondary tubercles 

 are, upon the whole, very varying in size and number; in some specimens they 

 form very conspicuous vertical series, in others they are all of almost uniform small 

 size, scarcely forming distinct vertical series. The aréoles of the primary inter- 

 ambulacral tubercles are small and, generally, not in contact, except a few of those 

 nearest the peristome; even at the ambitus they are separated by a series of miliary 

 tubercles. In the ambulacra the aréoles are generally in contact, probably always 

 at the ambitus, at least in larger specimens, sometimes along the whole series from 

 the peristome to the apical system. 



