GO 



radial bears upon one superior sloping side two secondarj'^ 

 radials and, upon the other, a single secondary radial, which 

 is axillary and supj^orts, on each superior sloping side, two 

 tertiary radials. which arrangement gives to each of these two 

 rays three arms. The other ray, in its normal condition, may 

 be like the last two, and if so. the species will have seventeen 

 arms, but in the specimen illustrated, it is different and is 

 peculiarly constructed, as follows. Upon one side of the third 

 primary radial there is a single secondary radial, which is 

 axillary and bears upon each superior side a single tertiary 

 radial, and, upon the other side of the third ]3rimary radial, 

 an interradial is su^jported, without the intervention of a 

 secondary radial, and, therefore, there are only two arms to 

 this ray, which gives us only sixteen arms in the specimen 

 illustrated, and, until it can be shown, that this structure is 

 abnormal, the species must be regarded as possessing only 

 sixteen arms. 



The first interradials are of unequal size, one of them is 

 heptagonal and each of the others has nine sides. The hep- 

 tagonal plate is followed by two plates, in the second range, 

 one of which rests, in part, on one of the superior sides of a 

 third primary radial and takes the position of a secondary 

 radial in the two-armed ray. These two plates in the second range 

 connect with two plates belonging to the vault. In the other 

 four areas, one plate, in the second range, is followed by one 

 in th(! third range that unites with two plates belonging to 

 the vault. 



The vault is moderately convex over tlie ambulacral canals 

 and correspondingly depressed in the interradial areas. It is 

 covered by a few rather large polygonal plates that bear pus- 

 tules, and each one over the junction of the ambulacral canals 

 bears a central node. The azygous orifice is central. No 

 ovarian ])()r(>s can l)e distinguished. 



We regard the interradial area having the first plate heptago- 

 nal as the azygous area, and, if the two-armed ray is abnor- 

 mal and the species has seventeen arms, then it will re.semble 

 D. aurealus, from whicli it will bo readily distinguished, by 

 the int(>rradial ari^as; for in that sjiecies. there are three plates, 

 in the third range, that unite with the plates of the vault, in 



